1A-M-P-01 Sep 7 - Afternoon (2:00-4:00 PM) Materials - Transport I |
Temperature dependence of the film cooling time deduced from the time of nucleation of a dissipative zone in a superconducting YBa2Cu3O7 Filament HARRABI Khalil1 1Physics Department, King Fahd University of Petroleum Minerals, Saudi Arabia show / hide abstract The application of an overcritical current pulse I>Ic(T) to narrow YBa2Cu3O7 strips generates a phase-slip center after a certain delay time td . By analyzing the function td(I/Ic) through a time-dependent Ginzburg-Landau theory, one can extract the cooling time of the film on its substrate. This parameter was found to remain constant from 5 to 40 K, but also found to increase notably above 40 K and up to Tc . We interpret this behavior as a manifestation of heat transfer by a blackbody radiation of acoustic phonons, and the loss of emissivity at higher temperatures to the rise of phonon-phonon interaction processes. K.H gratefully acknowledges the support of the King Fahd University of Petroleum and Minerals, Saudi Arabia, under the IN131034 DSR project. |
Electrical percolation in MgB2-La0.7Sr0.3MnO3 composites: evidence for a superconducting long-range proximity effect in the half-metallic manganite KONONENKO Victoria1, TARENKOV Vladimir1, BELOGOLOVSKII Mikhail2, SCHMIDT Stefan3, SEIDEL Paul3 1Donetsk Institute for Physics and Engineering, Ukraine, 2Institute for Metal Physics, Ukraine, 3Institut für Festkörperphysik, FSU Jena, Germany show / hide abstract Electrical percolation in MgB2-La0.7Sr0.3MnO3 composites: evidence for a superconducting long-range proximity effect in the half-metallic manganite Victoria Kononenko1, Vladimir Tarenkov1, Mikhail Belogolovskii2, Stefan Schmidt3, and Paul Seidel3 1 Donetsk Institute for Physics and Engineering, 03680 Kyiv, Ukraine It is known that spin-singlet superconducting (S) correlations, as well as triplet ones with zero spin projection, decay into an itinerant electron ferromagnetic (F) layer over a very short distance determined by the exchange energy. At the same time, a triplet component with a finite total spin generated at a magnetically inhomogeneous F/S interface may penetrate over a much longer distance limited only by temperature T. Although the long-range effect has been already observed for some F layers, up to now there is no consensus relating half-metallic manganites with 100% spin polarization where singlet superconducting correlations cannot exist.2 Institute for Metal Physics, 03680 Kyiv, Ukraine 3 Institut für Festkörperphysik, Friedrich-Schiller-Universität Jena, 07743 Jena, Germany We address this problem by studying transport characteristics of homogeneous composites formed by granules of a superconducting MgB2 on μm scale and those of La0.7Sr0.3MnO3 as small as 8-10 nm. The density of the composite with the relative volume fraction of superconducting grains p = 0.74 was as high as (96 ± 3) % of the theoretical value. Let us assume that the manganite grains form a sheath around MgB2 granules, then its average thickness would be ~ 350 - 700 nm. If the ferromagnetic manganite grains are completely impenetrable for superconducting correlations except ultra-thin sheath parts, the transition interval to an S-state would be very narrow while in our samples with p = 0.9 and 0.74 it was about 10 and 25 - 30 K, respectively. Moreover, at high pressures of 12 kbar, we have observed a shift of the midpoint in the resistance-vs-T curves to higher temperatures which can be explained by the enhancement of the superconducting proximity effect in hybrid contacts formed by superconducting MgB2 and ferromagnetic manganite components. Whereas in pure MgB2 the critical current, as well as the critical temperature Tc, was reduced under the pressure of 12 kbar, in our hybrid samples it increased. This work was performed within the German-Ukrainian project SE 664/18-1 supported by Deutsche Forschungsgemeinschaft (DFG). |
Oxygen Isotope Effects on Lattice Properties of La_{2-x}Ba_{x}CuO_{4} (x = 1/8) GUGUCHIA Zurab1, SHEPTYAKOV Denis2, POMJAKUSHINA Ekaterina3, CONDER Kazimierz3, KHASANOV Rustem1, SHENGELAYA Alexander4, SIMON A5, BUSSMANN-HOLDER Annette5, KELLER Hugo6 1Laboratory for Muon Spin Spectroscopy, Paul Scherrer, Switzerland, 2Laboratory for Neutron Scattering and Imaging, Paul Scherrer, Switzerland, 3Laboratory for Developments and Methods, Paul Scherrer, Switzerland, 4Department of Physics, Tbilisi State University, Georgia, 5Max Planck Institute for Solid State Research, Germany, 6Physik-Institut der Universitat Zurich, Winterthur, Switzerland show / hide abstract A novel negative oxygen-isotope (16O/18O) effect (OIE) on the low-temperature tetragonal phase transition temperature T_LTT was observed in the stripe phase of La_(2-x)Ba_xCuO_4 (x = 1/8) using high-resolution neutron powder diffraction. The corresponding OIE exponent alpha_(T_LTT) = - 0.36(5) has the same sign as alpha_(T_so) = -0.57(6) found for the spin-stripe order temperature T_so [1]. The fact that the LTT transition is accompanied by charge ordering (CO) implies the presence of an OIE also for the CO temperature T_co. Furthermore, a temperature dependent shortening of the c-axis with the heavier isotope is observed. These results indicate that all transitions observed in the stripe phase of La_(2-x)Ba_xCuO_4 (x = 1/8) are sensitive to oxygen lattice vibrations. The theoretical lattice dynamical calculations based on a dynamic anharmonic electron lattice interaction Hamiltonian consistently reproduce the experimental results. This structural instability is driven by phonon mode softening stemming from anharmonic electron-lattice interactions and these interactions are essential for the stripe formation in the cuprates. The present results may contribute to a better understanding of the complex microscopic mechanism of stripe formation and of high-temperature superconductivity in the cuprates in general. [1] Z. Guguchia, R. Khasanov, M. Bendele, E. Pomjakushina, K. Conder, A. Shengelaya, and H. Keller, Phys. Rev. Lett. 113, 057002 (2014). |
Effect of Terbium Substitution on Structure, Ru valence, and Magnetic Properties of RuSr2(Eu1.2Ce0.8)Cu2O10-δ LEE Ho Keun1, AHN Docheon2, KIM Yong-Il3 1Kangwon National University, South Korea, 2Pohang Accelerator Laboratory, South Korea, 3Korea Research Institute of Standards and Science, South Korea show / hide abstract Polycrystalline samples of RuSr2(Eu1.2Ce0.8-xTbx)Cu2O10-δ (0 ≤ x ≤ 0.3) (Ce/Tb samples) and RuSr2(Eu1.2-xTbxCe0.8)Cu2O10-δ (x = 0.3) (Eu/Tb sample) were synthesized by a solid-state reaction method. The samples were characterized by means of X-ray diffraction, Ru K-edge X-ray absorption spectroscopy (XAS), magnetization, and thermoelectric power measurements. It was found that Ce/Tb substitution resulted in a negligible change in the magnetic ordering temperature, Tm and a reduction of the weak-ferromagnetic component of the field-cooled (FC) magnetization as the Tb content increases, in contrast to the (Eu/Tb) sample which showed an increase in the magnetic ordering temperature with no prominent change in the FC magnetization at low temperatures. The XAS measurements indicated that substitution of Tb in both Ce/Tb and Eu/Tb samples caused an increase in Ru valence toward 5+. The magnetic properties are discussed in conjunction with the local structural changes in the Ru sublattice and the change in Ru valence induced by Tb substitution. This work was supported by a National Research Foundation Grant (NRF-2012R1A1A2042519) and by a 2015 research grant from the Kangwon National University. We express our thanks to the Korea Basic Science Institute for help with the SQUID measurements and to the Pohang Accelerator Laboratory for help with the XAS measurements. |
Influence of n-value and rise rate on the Magnetic Field Penetration in HTS Bulks DOUINE Bruno1, BERGER Kevin1, LEVEQUE Jean1, BONNARD Charles-Henri2, SIROIS Frederic2, KAMENI Abelin3 1Université de Lorraine, France, 2Ecole Polytechnique de Montreal, Canada, 3Université Paris Sud, France show / hide abstract The complete penetration magnetic field BP is a very important parameter of superconducting bulks submitted to an applied magnetic field. It is useful to know it for applications as superconducting permanent magnet synchronous motors. In this study, cylindrical HTS pellets were submitted to an axial applied magnetic field. Theoretical and experimental studies are presented. For numerical simulations, the E-J characteristic of HTS bulks was described by a power law relationship, i.e. E(J) = EC(J/JC)n. The influence of the n-value and of the rising rate Vb of the applied field on the BP of HTS cylindrical pellets was investigated, and a linear relationship between BP, Vb and n-value could be established. The experiment was based on direct measurements of the local magnetic field in the gap between two bulk HTS pellets. The measurements of the field penetration has been carried out on HTS pellets at 77 K by applying increasing axial magnetic fields with a quasi-constant sweep rate. The influence of the gap size between the two HTS pellets was studied with a particular attention. Two values of the complete penetration field BP have been measured at two different rising rates Vb, allowing n-value determination. We conclude that using a combination of measurements and numerical simulations allow determining in a quite simple way the n-value and the critical current density JC of real HTS pellets. |
Superconductivity in Iridium based compounds CaIr2 and SrIr2 YANPENG Qi1, CLAUDIA Felser1 1Max Planck Institute for Chemical Physics of Solids, Germany show / hide abstract Iridium is one of interesting 5d elements and a wide variety of physical properties at low temperature are observed in iridium related compounds. It is believed that electron correlations and spin-orbit copping play an important role in determining their electronic properties. Here we report the synthesis, experimental electronic characterization, and calculated electronic band structure of the cubic Laves phase superconductor CaIr2 (Tc = 6.1K) and SrIr2 (Tc = 5.8 K), which the Ir atoms have a pyrochlore lattice. The presence of a bulk superconducting transition was confirmed, and the properties of the superconductor were elucidated through magnetization and heat capacity measurements. The electronic band structure calculations indicate that the the Ir d states are dominant through the Fermi level. At last the effects of spin-orbit coupling in the Ir based compounds on the electronic structure, even the existence of superconductivity are discussed. |
Trapped magnetic-field property and microstructure of highly dense MgB2 bulk doped with Ti YOSHIDA Takafumi1, MOCHIZUKI Hidehiko1, FUJISHIRO Hiroyuki1 1Iwate University, Japan show / hide abstract MgB2 superconductors have mainly been studied for the practical application for tapes and thin films owing to high Tc of about 39 K and high upper critical field among metallic superconductors. We have studied that the trapped field properties of MgB2 bulks fabricated by the capsule and hot isostatic pressing (HIP) methods and succeeded in producing the 2-3 T class bulk magnet. Recently, the trapped field of 5.4 T was reported for the hot-pressed MgB2 bulk using the mechanical alloyed precursor powder [1]. In this paper, to obtain the higher trapped field we studied the doping effect of Ti on the trapped field in MgB2 bulks fabricated by the HIP method. The (Mg1-xTix)B2 bulks were magnetized by the field cooling magnetization (FCM) in a magnetic field of 10 T using a 10-T cryogen-free superconducting magnet. The highest trapped field at the top surface of the single bulk (x=0.1) was 3.6 T and that at the center between the doubly stacked bulks (x=0.05 and 0.1) was 4.6 T. We discuss precisely the effect of Ti on the enhancement of the vortex pinning from the analysis of the microstructure observed by an electron backscatter diffraction method. [1] G. Fuchs et al, Supercond. Sci. Technol. 26 (2013) 122002. |
Flux jumps in pulse magnetized HTS annuli KOROTKOV Vasily1, KRASNOPEROV Evgeniy2, KARTAMYSHEV Alexander1 1National research Center "Kurchatov Institute", Russia, 2Moscow Institute of Physics and Technology, Russia show / hide abstract Pulse Field Magnetization is the most preferable method of field activation of HTS magnets. A serious drawback of this method is a substantial warming, and as a consequence, the occurrence of flux jumps. In this work the flux jump process were examined on melt-grown YBCO-annuli with outer diameter of 36 mm and inner diameter of 17 mm. A single pulse procedure was realized. The appearance of the jump depends on the pulse amplitude and its duration. At low amplitude the field trapped in the hole increases monotonically. At some critical amplitude the trapped field falls sharply (flux jump) and even changes sign. With further increase of the amplitude the trapped field remains negative and small. When pulse duration decreases the flux jump is observed at lower pulse amplitude. We believe that the critical parameter - Ha/t regulates the flux jump. Flux jump occurs due to the destruction of the circular shielding currents. The measurement of the radial distribution of the longitudinal magnetic field component Bz(r) after the flux jump shows that the annulus body is magnetized along the external field and the field in the hole has the opposite direction. The flux jump takes place when the circulating critical currents is insufficient to shield the rapid variation of the external magnetic field. Authors thank Russian Fund for Assistance to Small Innovative Enterprises in Science and Technology for financial assistance. |
Influence of soft ferromagnetic materials on the magnetic flux density above large grain, bulk high temperature (RE)BCO superconductors: measurements and modelling PHILIPPE Matthieu1, AINSLIE Mark2, FAGNARD Jean-Francois1, WÉRA Laurent1, DENNIS Anthony2, SHI Yunhua2, CARDWELL David2, MORITA Mitsuru3, NARIKI Shinya3, TESHIMA Hidekazu3, VANDERHEYDEN Benoit1, VANDERBEMDEN Philippe1 1SUPRATECS, University of Liège, Belgium, 2Bulk Superconductivity Group, Univ. of Cambridge, United Kingdom, 3Nippon Steel & Sumitomo Metal Corporation, Japan show / hide abstract Due to their ability to trap high magnetic fields, bulk (RE)BCO superconductors can be used as powerful permanent magnets in various engineering applications such as rotating machines and magnetic bearings. We combine soft ferromagnetic pieces with bulk, large grain (RE)BCO high temperature superconductors to form superconductor/ferromagnet (SC/FM) hybrid structures. We study how the ferromagnetic pieces influence (i) the profile shape of the trapped magnetic flux density at the surface of each structure and (ii) the decrease of the trapped field under an applied field that is orthogonal to the main magnetization (crossed field configuration). Hall probe mappings of the trapped magnetic flux density profile above the hybrid structures at 77 K are compared to modelled profiles using a 2D finite element method. Modelling results are in excellent qualitative and quantitative agreement with the measurements. The model is then used to study the magnetic flux distribution and predict the behaviour for other constitutive laws and ferromagnet geometries. For the modelled configurations, the magnetic flux density is enhanced on the face opposite to the ferromagnet. Both thickness and saturation magnetization of the ferromagnetic material are found to be important parameters. The saturation regime of the ferromagnet can be predicted using a simple analytical model. We show that thin ferromagnetic discs can be driven to full saturation even though the superconductor magnetic field is much smaller than their saturation magnetization. Remarkably, the beneficial influence of the ferromagnet on the trapped field can be observed even if the trapped flux density above the superconductor is much larger than the ferromagnet saturation magnetization. Finally, we show that the ferromagnetic material acts as a magnetic shield and lowers the relative demagnetization effect caused by the application of transverse (crossed) magnetic field cycles. This work is part of an Action de Recherches Concertées grant from the Ministry of Higher Education through the Research Council of the University of Liege (ARC 11/16-03). |
Selective magnetic field invasion into HTS bulk magnets in pulse field magnetizing processes OKA Tetsuo1, HARA Kensuke1, OGAWA Jun1, FUKUI Satoshi1, SATO Takao1, YOKOYAMA Kazuya2, MURAKAMI Akira3, LANGER Marco4 1Niigata University, Japan, 2Ashikaga Institute of Technology, Japan, 3Ichinoseki National College of Technology, Japan, 4IFW Dresden, Germany show / hide abstract The selective motions of the magnetic flux invasion into the Dy123-based HTS bulk magnets were experimentally evaluated during the pulsed field magnetization PFM processes. The flux motion and resultant trapped magnetic flux densities were measured at the surface center of the bulk sample at the temperature of 30 K. The invasion of the magnetic flux into the sample is expected to be affected by the microscopic structure and the geometrical distribution of the Jc values, we estimated the differences between the magnetic flux motions between those in the regions of growth sector boundary GSB and growth sector region GSR by measuring the magnetic flux density and temperature changes during the pulsed field application of 5-T in the superconducting state. The experimental results showed us that the magnetic flux invades into the sample through the path in the GSR earlier than that in the GRB region, which clearly reflects the different Jc values in each region. Furthermore, the data of flux-invading speed gradually changed according to the positions on the GSR, while the data irregularly changed on the GSB. This means that the direction of magnetic flux does not uniformly flow on this area. Since the temperature on the path of magnetic flux changes more rapidly than those in other regions, we can trace the invasion path of magnetic flux. As a result, the heat generation due to the invading flux motion occurs in the GSR region prior to the GSB region. Thus, the magnetic flux invasion behavior exhibits selective and non-uniform motion reflecting the difference of the macrostructure. The authors give thanks to Dr. Teshima of Shinnittetsu-Sumikin Co. for his assistance. |
Overcoming the adverse effects of granularity on the critical current density in iron-based superconductors HECHER Johannes1, BAUMGARTNER Thomas1, WEISS Jeremy2, JIANG Jianyi2, KAMETANI Fumitake2, TARANTINI Chiara2, HELLSTROM Eric2, LARBALESTIER David2, HAYASHI Yujiro3, YAMAMOTO Akiyasu3, SHIMOYAMA Jun-Ichi3, EISTERER Michael1 1Atominstitut, Vienna University of Technology, Austria, 2NHMFL, Florida State University, United States, 3Dept. of Appl. Chemistry, The University of Tokyo, Japan show / hide abstract Recent results obtained from iron-based high-temperature superconductors are promising in terms of performance, however, major improvements are still necessary for these materials to become competitive. Our experimental data and the model we developed to describe them suggest a strategy for achieving this performance boost. We studied the field dependence of the critical current density in Co- and K-doped Ba-122 polycrystals with different grain sizes. The use of SHPM (Scanning Hall Probe Microscopy) allowed us to directly visualize the magnetization profiles of the samples, from which the macroscopic critical current density as well as the currents flowing within the grains can be inferred. By performing SHPM measurements at various values of applied field, we were able to track the complex evolution of the magnetization profiles, which exhibit a pronounced dependence on the magnetization history. We present a model explaining this evolution and hence the history effect in the critical current density, which is based on the assumption that adjacent grains are coupled by Josephson currents. Within the framework of this model the macroscopic critical current density results from the interplay of intra-granular currents with these Josephson currents. Fitting the free parameters of this model to data obtained from SHPM measurements and from SQUID magnetometry results in very good agreement with these data and realistic values of the free parameters (the maximum inter-granular current density and the average thickness of the Josephson junctions). An important prediction of this model, which is also supported by our experimental data, is that the in-field macroscopic critical current density increases with decreasing grain size. This result may pave the way towards a significant improvement of the performance of granular high-temperature superconductors. |
Superconducting and hybrid systems for magnetic field mitigation GOZZELINO Laura1, GERBALDO Roberto1, GHIGO Gianluca1, LAVIANO Francesco1, AGOSTINO Angelo2, BONOMETTI Elisabetta2, TRUCCATO Marco2 1Politecnico di Torino and INFN Sez. Torino, Italy, 2University of Torino and INFN Sezione di Torino, Italy show / hide abstract Magnetic field shielding is crucial for several applications requiring an ultralow magnetic field environment (e.g. biomedical application) or the mitigation of the magnetic field produced by an electronic device in order to guarantee electromagnetic compatibility with the surrounding environment or to prevent possible health hazards (e.g. workers safety). In this framework, we investigated the efficiency of superconducting (SC) MgB2 and hybrid MgB2/Fe systems of different shapes (disk, tube, cup) for magnetic field mitigation. Shielding capability of these systems was measured as a function of temperature, external magnetic field, position and time by means of cryogenic Hall probes mounted on a custom-designed stage, moveable along the sample axis with micrometric resolution [1]. In all the investigated configurations, the presence of the ferromagnetic (FM) layer allows tuning the shielding efficiency of the superconductor. In particular, these hybrid systems result the most efficient solutions at applied fields higher than 0.5 T , where the use of SC/FM coaxial cups allow obtaining a shielding efficiency 3-4 times higher than that measured with a single MgB2 cup, coupled with a reduction of the flux creep phenomena. On the contrary, at low field, the only superconducting solution is the most efficient. Starting from these results, further shielding solutions, obtained by numerical simulations, are proposed in order to achieve additional improvements in the shielding efficiency of these hybrid systems, optimizing the relative sizing of the SC and FM layers and the air gap width between them. [1] L. Gozzelino et al., Supercond. Sci. Technol. 25, 115013 (2012). Authors wish to thank F. Gomory for fruitful discussions. This work was partially supported by the National Institute for Nuclear Physics under SR2S-RD experiment. |
Trapped field in bulk MgB2 superconductor fabricated by Spark Plasma Sintering GOZZELINO Laura1, CAPUTO Jean-Guy2, GERBALDO Roberto1, NOUDEM Jacques3, GHIGO Gianluca1, DUPONR Louis4, LAVIANO Francesco1, BERNSTEIN Pierre3 1Politecnico di Torino, Italy, 2INSA de Rouen, France, 3Université de Caen-Basse-Normandie, France, 4CAYLAR, France show / hide abstract The capability of MgB2 bulks to trap high magnetic fields at temperatures around 20K could find applications in the domain of scientific equipment, for example for manufacturing small size high field permanent magnets. It was previously reported that a 2.6T field could be measured between two 25mm diameter MgB2 bulks at 20K [1]. In this contribution, we report measurements of the trapped field above 20mm diameter MgB2 bulks after the application and the removal of magnetic fields ranging between B=0T and B=4T and at temperatures between 20K and 32.5K. The bulk MgB2 superconductors were fabricated by unconventional Spark Plasma Sintering (SPS) technique resulting in a very high relative density. For each temperature and field the trapped field was measured with 8 small Hall probes located along a diameter of the samples. The measurements were carried out i) as a function of time after the applied field zeroing and ii) as a function of the distance to the sample surface.The measurements as a function of time have shown a strong magnetic relaxation occurring immediately after the removal of the magnetic field. Stabilization occurs after a few thousands seconds. The field stabilized value was then measured as a function of the distance to the samples. While trapped field up to 1.6T was measured at a 1.5mm distance above samples after the application of a 3T magnetic field at 20K, the application of higher fields did not result in an increase of the trapped field. This suggests that at high field current lines with a density equal to the critical value flow in the whole bulk while they flow in a fraction of the samples at lower fields. Based on this result, the measurements recorded by various probes were reproduced with numerical techniques and those measured above the center of the bulks also by analytical considerations. Both methods have resulted in similar values for the critical current density at the different measurements temperatures. [1] J.Durrel at al. Supercond. Sci. Technol. 25 (2012) 112002 The work of Louis Dupont was partially funded with a CIFRE grant of Agence Nationale de la Recherche et de la Technologie. |
Demagnetization Delusion: Mixed State Shape Effect and its Peculiar Features OH Sangjun1 1National Fusion Research Institute, South Korea show / hide abstract Magnetic fields are partially penetrated into a type II superconductor in the form of quantized vortices. Extrinsic pinning current flows together with intrinsic supercurrent. How the field is distorted by these currents has never been clearly discussed. Here, we report that mixed state shape effect is quite different from demagnetization effect. It was shown that peculiar features of irreversible magnetization, for example, a very steep magnetization slope, can be understood by shape dependent magnetization magnification. Reversible magnetization in the presence of vortices is a bit more complicated. Intrinsic current contribution at the edges of vortices near the surface is found to be very crucial, for example, for empirically observed magnetization orientation variations. More detailed free energy study, including the vortex-edge effect seems to be necessary. This work was supported by Mid-career Researcher Program through NRF grant funded by the Ministry of Education, Science & Technology (MEST) (No. 2010-0029136). |
Explanation of the magnetic stiffness performance of Multi–Seeded YBCO with graded changing of PM pole direction OZTURK Kemal1, ABDIOGLU Murat2, KABAER Mehmet1 1Faculty of Science, Karadeniz Technical University, Turkey, 2Faculty of Education, Bayburt University, Turkey show / hide abstract As known, in superconductor Maglev and bearing system not only magnetic levitation but also magnetic stiffness are very critical parameter for industrial applications. In performed studies in literature, the vertical and lateral magnetic stiffness values of YBCOs could not be increased at the same time, because of different cooling process, even though some improvements of these stiffness have been achieved individually. In our study, we investigated vertical and lateral magnetic stiffness properties of multi–seeded YBCO bulk depending on the magnetic pole direction in PMG (Permanent magnet guideway) and different vertical position of onboard PM in different CHs to achieve larger vertical and lateral stiffness values together. Firstly, the vertical and lateral stiffness measurements were performed between multi–seeded YBCO and two type PMG with three PM vertical pole direction to understand physical mechanism of the magnetic stiffness and stability in different cooling height after the magnetic flux distributions modelling of PMG. Then, to enhance stiffness parameter and investigate applicability of multi–seeded YBCO for Maglev system the vertical and lateral magnetic stiffness measurements were carried out between multi–seeded YBCO and different PMGs (Conventional and Halbach PMG) depending on additional downward PMs in Conventional PMG and the onboard PM positions in onboard unit for different CHs. In our study, it has seen that the both vertical and lateral magnetic stiffness have different properties for different magnetic pole direction and relating stiffness values increases gradually with additional downward PMs and optimal onboard PM position. This work was supported by the Scientific and Technological Research Council of Turkey (TÜBITAK), with project no. 112T090 and the Scientific Research Project Fund of Karadeniz Technical University in Turkey, with project no. 11060. |
Superconductivity in In doped topological crystalline insulator SnTe MAURYA Vishal1, SHRUTI 1, PATNAIK Satyabrata1, SRIVASTAV Pankaj1 1School of physical Sciences , India show / hide abstract Superconductivity in In doped topological crystalline insulator SnTe Vishal Kumar Maurya, Shruti and Satyabrata Patnaik School of Physical Sciences, Jawaharlal Nehru University - New Delhi, India Abstract – Here we want to report the superconducting properties of recently discovered superconductor Sn0.5In0.5Te, derived from well-known topological insulator SnTe. Crystals were grown using modified Bridgman technique in a vertical tube furnace at temperature gradient zone. Further XRD and Rietveld refinement has been done to determine the phase purity of the sample. We found superconducting transition temperature Tc at 4.5 K in the resistivity measurement done from 1.6-300K temperature range. Zero-Field cooled and Field cooled measurement have confirmed bulk superconductivity at same Tc. Upper critical field has been found to be 1.6 T from WHH formula. Coherence length has been found to be 143.5 Å. Hole conduction in the crystal has been found by Seebeck and Hall coefficient measurement performed on the sample crystal. Lowering of the superconducting transition temperature has been found lowered monotonically on applying pressure upto 3 Gpa. VKM, Shruti, and PS acknowledge the UGC (India) for providing UGC-BSR, UGC-SRF, and UGC-DS Kothari fellowships, respectively. Technical support from AIRF (JNU) is gratefully acknowledged. SP would like to acknowledge financial support from DST-PURSE and DST-FIST programs of Department of Science and Technology (Government of India) |
Interfacial intrinsic exchange field in a conventional BCS superconductor PAL` Avradeep1, BLAMIRE Mark1 1University of Cambridge, United Kingdom show / hide abstract Proximity effect of a ferromagnetic insulator / Superconductor hybrid is studied by means of measuring differential conductance of NbN/GdN/TiN superconductor / ferromagnetic insulator / normal metal junctions. The data shows for high spin polarization of the GdN layer1 a large zero-field voltage offset interpreted as a spin-filtered Zeeman splitting of the NbN density of states by an effective exchange field (H0) from the GdN. The splitting increases linearly with applied field (Hext) enabling the relative sign of H0 and Hext to be determined. We show that the short NbN coherence length concentrates H0 at the NbN/GdN interface and eliminates any averaging over the GdN domain structure. Presence of large exchange field in the superconductor points to existence of unconventional superconductivity in an otherwise normal s-wave superconductor, and sheds light on the unconventional second harmonic current phase relation of corresponding NbN/GdN/NbN Josephson junctions 2,3. 1. Pal, A., Senapati, K., Barber, Z. H. & Blamire, M. G. Electric-Field-Dependent Spin Polarization in GdN Spin Filter Tunnel Junctions. Adv. Mater. 25, 5581–5 (2013). 2. Pal, A., Barber, Z. H., Robinson, J. W. A. & Blamire, M. G. Pure second harmonic current-phase relation in spin-filter Josephson junctions. Nat. Commun. 5, 3340 (2014). 3. Senapati, K., Blamire, M. G. & Barber, Z. H. Spin-filter Josephson junctions. Nat. Mater. 10, 849–52 (2011). |
1A-M-P-02 Sep 7 - Afternoon (2:00-4:00 PM) Materials - Pnictides I |
Study of Sn addition on the intergranular critical current density in polycrystalline Sm1111 iron-pnictides SINGH Shiv1, HAYASHI Kosuke2, OGINO Hiraku2, KISHIO Kohji2, SHIMOYAMA Jun-Ichi2 1IFW Dresden, Germany, 2The University of Tokyo, Japan show / hide abstract The low value of the intergranular Jc measured in polycrystals is the principal obstacle to applications of pnictide superconductor (RE1111; REFeAsO; RE = rare earth) and the concern that grain boundaries are weakly coupled with each other. To reduce this problem, we have synthesized a series of Sn added Sm1111 (SmFeAs(O,F) + xSn; x = 0-0.8) polycrystalline samples by low temperature synthesis method and studied the influence of the Sn addition on the intergranular Jc of Sm1111. These samples are well characterised by various measurements, such as XRD, Field Emission Scanning Electron Microscope (FESEM), resistivity under magnetic fields, magnetic susceptibility and remanent magnetization. Powder XRD measurements revealed the purity of the samples and showed that the lattice volume slightly increases with the Sn addition in the lightly F doped Sm1111 (SmFeAsO0.88F0.12), suggesting the reduced of fluorine concentrations inside the lattice, whereas there is almost no change in the lattice volume of the optimally doped sample (SmFeAsO0.8F0.2). The transition temperature (Tc) of lightly F doped Sm1111 (Tc = 51 K) shifted to lower temperature and reached to 40 K for 40% Sn addition. On the other hand, optimally F doped Sm1111 (Tc = 57 K) have the almost same value of Tc with Sn addition. Microstructural analysis depicts that the impurity phases in SmFeAsO0.8F0.2 reduced with Sn addition and, clean and well-connected grain boundaries increased. The Sn added SmFeAsO0.8F0.2 samples have the onset Tc up to 57 K and the intergranular Jc of over 104 A cm-2 at 5 K in the self-field, as assessed by remanent magnetization measurements. Sn addition improves the intergranular Jc of Sm1111 from 200 to 11000 A cm-2 for 20% fluorine doped and 4000 to 9700 A cm-2 for 12% fluorine doped samples respectively. We believe this superior intergrain Jc to be attributable to the strong intergrain coupling due to grain connectivity improved by the Sn addition. In addition, we will also discuss the optimization of the synthesis of Sn added Sm1111 below our conventional temperature (900°C) where the polycrystalline samples sintered at 750°C showed the intergrain Jc of over 3000 A cm-2 at 5 K. Reference: S. J. Singh et al., Supercond. Sci. Tech. 27, 085010 (2014) and 26, 065006 (2013). SJS thanks the Japan Society for the Promotion of Science (JSPS) and German Academic Exchange Service (DAAD) for JSPS and DAAD Postdoctoral Fellowships for Foreign Researchers, respectively. |
Improvement of transport critical current density in SmFeAsO1-xFx tapes by ex-situ powder-in-tube method ZHANG Qianjun1, MA Yanwei1, ZHANG Xianping1, YAO Chao1, LIN He1, WANG Dongliang1, DONG Chiheng1, AWAJI Satoshi2, WATANABE Kazuo2 1Chinese Academy of Sciences, China, 2Tohoku University, Japan show / hide abstract Iron-based superconductors have enormous potential for high field magnet applications, since they have very high upper critical field, large critical current density (Jc), relatively small anisotropy and strong intrinsic pinning. Among the main families of iron-based superconductors, 1111 family attracted much interest for application as it has the highest transition temperature of 56 K. The wire fabrication study by powder-in-tube method of 1111 families had begun very early. However, the transport critical current density was severely limited by many difficulties including grain connectivity, fluorine control and impurity control. We are aimed to solve these problems. A Sn-presintering process of the SmFeAsO1-xFx precursor powder was applied. The intergranular Jc in SmFeAsO1-xFx tape was greatly improved, which was confirmed by transport current measurement and Magneto-optical imaging. Moreover, a series of low-temperature (300-500 °C) heat treatments under ambient pressure or uniaxial pressure were performed on SmFeAsO1-xFx tapes, which effectively avoided fast fluorine loss in tapes and prevented reaction layers between superconducting core and sheath metal. A highest transport Jc of 3.95 × 104 A cm-2 (at 4.2 K and self-field) is achieved in SmFeAsO1-xFx tapes. This work was supported by the National “973” Program (Grant No. 2011CBA00105), National Natural Science Foundation of China (Grant Nos. 51025726, 51320105015 and 51202243), and China-Japan Bilateral Joint Research Project by NSFC and JSPS. |
Hydrostatic pressure: A very effective approach to significantly enhance critical current density by orders of magnitude in iron pnictide superconducting tapes, granular bulks and single crystals WANG Xiaolin1 1University of Wollongong, Australia show / hide abstract We present our study on the effect of hydrostatic pressure (applied during measurements) on the significant enhancement of flux pinning, Jc, and Tc in polycrystalline pnictide bulks, tapes and single crystals of Sr4V2O6Fe2As2, NaFe0.972Co0.028As, Ag-clad Sr0.6K0.4Fe2As2 tape with Sn addition, respectively. We demonstrate that the hydrostatic pressure up to 1.2 GPa can not only greatly increase Tc from 15 K (underdoped) to 22 K, but also significantly enhance the irreversibility field, Hirr, by a factor of 4 at 7 K, as well as the critical current density, Jc, by up to 30 times at both low and high fields for Sr4V2O6Fe2As2 polycrystalline bulks. Jc in NaFe0.972Co0.028As single crystals can be enhanced by at least tenfold at low fields and more than a hundredfold at high fields with Tc raising from 18 up 24 K. Remarkbly, Our team has found that hydrostatic pressure of 1.1GPa can significantly enhance Jc in Sr0.6K0.4Fe2As2 tapes by over an order of magnitude at both low and high fields with littile change in Tc. Record high Jc were obtained in the Ag-clad Sr0.6K0.4Fe2As2 tape under the hydrostatic pressure with valuves as high as 106 A/cm2 at low field and 1.8 × 105 A/cm2 at 13 T at 4K, which is roughly two times higher as compared to NbSn3. pinning is found to be dominant in all the samples under the hydrostatic pressure. Our flux pinning analysis indicates that the hydrostatic pressure can induce extra point defect pinning centers and increase the pinning force greatly, being mainly responsible for the significant Jc enhancement in all samples. In addition, a transformation from surface pinning to point pinning induced by pressure was accompanied by a reduction of anisotropy at high temperatures in granular samples. Our findings indicate that there are still plenty of room to further increase Jc in Fe-based superconductring tapes/wires, and also provide an effective method to significantly enhance Tc, Jc, Hirr, and Hc2, for other families of Fe-based superconductors in the forms of wires/tapes, films, and single crystals and polycrystalline bulks. The condensation energy enhanced by pressure which is in turn related to the pinning potential and Jc enhancement will be presented. This work is supported by Australian Research Council throught ARC Discovery project on Fe-based superconductors. |
Influence of the crystal growth regime on the properties of CuxTaS2 single crystals. ANTAL Vitaliy1, KAVECANSKY Viktor1, KOVAC Jozef1, PIOVARCI Samuel1, DIKO Pavel1 1Institut of Experimental Physics, Slovakia show / hide abstract The single crystals of CuxTaS2 were grown via chemical vapor transport method in evacuated quartz tube with iodine. Different crystal growth regimes were used for producing of several CuxTaS2 crystals. All copper intercalated TaS2 single crystals were prepared from the same powder composition at the beginning of the crystal growth. The structural characterization results show, that the growth regime could have a significant influence on the stoichiometry of the sample and their superconducting properties. In our work, we investigated properties of CuxTaS2 single crystals by Scanning Electron Microscopy, X-ray analysis, SQUID magnetization measurements as well as thermal analyses. This work was realized within the framework of the projects: VEGA 0090/13, APVV 0330/12, APVV Stefanik Project SK-FR-2013-0025, PHYSNET ITMS: 26110230097. |
Fabrication of Large and High-Performance FeSe Bulk Superconductors by a Simple Liquid–Solid Diffusion Method WANG Lei1 1Northwest A&F University, China show / hide abstract FeSe polycrystalline superconductors with dimensions over 10 × 10 × 3 mm3 were fabricated by diffusing liquid Se into an iron tablet at 650 °C. Scanning electron microscopy and X-ray diffraction analyses were performed on the FeSe samples, and they showed that the main phase throughout the bulk is tetragonal β-FeSe and the grains are well crystallized and connected. The critical transition temperature (onset) was determined to be 12 K, with a transition width of 3 K, by a resistivity measurement. The upper critical fields Hc2(0) was estimated to be 40 T, and the intragranular critical current density estimated from the Bean model is about 1.5 × 105 A/cm2 at 4 K in self-field. These results suggest that liquid-solid diffusion is a promising technique for fabricating large and high-quality FeSe bulk superconductors. |
High Critical Current Density in FeSe0.5Te0.5 Thin Films on CaF2 Substrate HANAWA Masafumi1, TSUKADA Ichiro1, NABASHIMA Fuyuki2, IMAI Yoshinori2, MAEDA Atsutaka2, POLYANSKII Anatolii3, TARANITINI Chiara3, LARBALESTIER David3 1Central Research Institute of Electric Power Industry, Japan, 2The University of Tokyo, Japan, 3The National High Magnetic Field Laboratory, Florida State University, United States show / hide abstract It is well known that iron pnictides and chalcogenides form a large variety of Fe based superconductors (FBS). Among FBS, iron chalcogenide superconductors has the simplest crystal structure which consists of only Fe2Ch2 (Ch = chalcogen) planes. Comparing with the other FBS, iron chalcogenide superconductors show lower superconducting critical temperature, Tc. However, the Tc of iron chalcogenide is easily modified by adding isotropic pressure or chemical intercalation. And also iron chalcogenides are known to indicate high upper critical field of superconductivity, Hc2. Because iron chalcogenides can be a good candidate for application use, research on critical current density (Jc) of this materials is essential. We have performed comprehensive and thorough research on substrate dependence of Fe(Se1-xTex) thin films grown by pulsed laser deposition. Throughout the surveys, we have confirmed that CaF2 substrate is the most appropriate for realizing fine superconducting properties of grown thin films. Critical current density (Jc) of FeSe0.5Te0.5 thin films on CaF2 substrates were evaluated by result of magneto-optical (MO) observation and I-V characteristic measurements. The Jcs of the thin films obtained from MO observation (3.3×106 A/cm2 at 7.4 K) and I-V characteristic (2.1×106 A/cm2 at 7.0 K) show one of the highest values ever reported for superconducting thin films of iron chalcogenides. Besides, it implies homogenous critical current density that a typical rooftop pattern is observed by MO imaging. Since angular dependence of Jc under magnetic field can be understood as that for anisotorpic 3D superconductors by using effective magnetic field, Heff = H·sqrt(sin2A+r-2cos2A) , with mass anisotropy ratio r = 1.8, the thin film is considered not to have any extra pinning mechanism. In conclusion, FeSe0.5Te0.5 thin films on CaF2 substrates demonstrate homogenous distribution of high Jc which is feasible for applications. |
Exploring the critical aspects in the fabrication of superconducting Ba0.6K0.4Fe2As2 ex-situ P.I.T. tapes MALAGOLI Andrea1, WIESENMAYER Erwin2, JOHRENDT Dirk2, GENOVESE Alessandro3, PUTTI Marina4 1CNR-SPIN, Italy, 2Ludwig-Maximilians-Universität, Germany, 3King Abdullah University of Science and Technology, Saudi Arabia, 4Department of Physics, University of Genova, Italy show / hide abstract Among the recently discovered Fe-based superconducting compounds, the (K,Ba)Fe2As2 phase is raising large interest within the scientific community, because together with its pretty high TC, high and nearly isotropic upper critical field HC2 and its large critical current density weakly dependent on the magnetic field has shown to be not strongly affected by weak link at the grain boundaries. In fact, after some years of development, critical current densities Jc of about 105 A/cm2 at fields up to more than 10 T have been obtained in power in tube (PIT) processed wires and tapes. Here we explore the crucial points in the wire/tape fabrication by means of the ex-situ PIT method. We focus on a scaling up processes which are crucial for the industrial fabrication. In particular, we have addressed the issues concerning the phase purity, the internal porosity and crack formation in the superconducting core region. An extensive microstructural analysis correlated with the transport properties has been carried out as well. We performed the heat treatment without any additional external pressure, observing that, in these conditions, temperatures higher than 800 °C led to the formation of a secondary non-superconducting phases. We also pointed out how the brittleness of the superconducting compound is a crucial point for the cold working. Our best conductors with a filling factor of about 30% exhibited Tc= 38 K the highest value measured in such kind of superconducting tape. The microstructure analysis show clean and well connected grain boundaries but rather poor density: The measured Jc of about 3∙104 A/cm2in self-field is suppressed by less than a factor 7 at 7 T. Such not extremely high Jc values can be accounted for by the reduced density while the moderate in-field suppression and a rather high n-factor confirm the high homogeneity and uniformity of these tapes. This work has been supported by FP7 European project SUPER-IRON (grant agreement No.283204) and “Compagnia di SanPaolo”. We thank Dr. Alice Scarpellini and Dr. Cristina Bernini for the help on scanning electron microscopy images acquisition. |
Thermodynamic stability of Co-doped BaFe2As2/SrTiO3 heterostructures KANG Jong-Hoon1, CAMPBELL Neil1, XIE Lin2, JIANG Jianyi3, WEISS Jeremy3, WANG Yi4, LIU Zi-Kui4, HELLSTROM Eric3, LARBALESTIER David3, PAN Xiaoqing2, RZCHOWSKI Mark1, EOM Chang-Beom1 1University of Wisconsin-Madison, United States, 2The University of Michigan, Ann Arbor, United States, 3Applied Superconductivity Center, NHMFL, FSU, United States, 4The Pennsylvania State University, United States show / hide abstract The discovery of high-Tc Fe-based materials has catalyzed a revitalization in the field of superconductivity. However, it is remarkably little known about interfacial phenomena between non-perovskite superconductors and perovskite oxides. Among iron based superconductors, Co-doped BaFe2As2 can offer an ideal platform for studying the fundamental physics of superconductivity because these are much more chemically stable with well optimized growth technique [1,2]. It is now well established that the iron arsenides can have superconducting behavior which is induced by chemical substitution or pressure [3]. Here we report a kinetic and thermodynamic study of growth mechanisms in Co-doped BaFe2As2/SrTiO3 heterostructures. To get further insight into the initial stages of thin film growth, first principles calculations can predict the ground state of BaFe2As2 growth on a SrTiO3 substrate. They suggest a thermodynamically stable reaction layer between film and substrate. Additional structural and chemical analyses were performed by scanning transmission electron microscopy and electron energy loss spectroscopy. We believe that the interface structure can be tailored to optimize Fe-based superconducting thin films with various perovskite oxide substrates. Such studies can also suggest further research on the interface between non-perovskite and perovskite materials. [1] S. Lee, J. Jiang, Y. Zhang, C.W. Bark, J. D.Weiss, C. Tarantini, C. T. Nelson, H.W. Jang, C. M. Folkman, S. H. Baek, A. Polyanskii, D. Abraimov, A. Yamamoto, J.W. Park, X. Q. Pan, E. E. Hellstrom, D. C. Larbalestier, and C. B. Eom, “Template engineering of Co-doped BaFe2As2 single-crystal thin films”, Nature Mater. 9, 397 (2010) [2] S. Lee, C. Tarantini, P. Gao, J. Jiang, J. D.Weiss, F. Kametani, C. M. Folkman, Y. Zhang, X. Q. Pan, E. E. Hellstrom, D. C. Larbalestier and C. B. Eom, “Artificially engineered superlattices of pnictide superconductors”, Nature Mater. 12, 392 (2013) [3] S. Kimber, A. Kreyssig, Y. Zhang, H. Jeschke, R. Valentí, F. Yokaichiya1, E. Colombier, J. Yan, T. C. Hansen, T. Chatterji, R. J. McQueeney, P. C. Canfield, A. Goldman, and D. N. Argyriou, “Similarities between structural distortions under pressure and chemical doping in superconducting BaFe2As2”, Nature Mater. 8, 471 (2009) Work at the University of Wisconsin was supported by the DOE Office of Basic Energy Sciences under award number DE-FG02-06ER46327. The work at NHMFL was supported under NSF Cooperative Agreement DMR-1157490 and DMR-1006584. |
SmFeAsO1-xFx and NdFeAsO1-xFx Thin Films by a Two-Step Method: Metalorganic Chemical Vapor Deposition and Arsenic Diffusion Processes CORRALES-MENDOZA Iván1, CONDE-GALLARDO Agustin1 1Centro de Investigacion y de Estudios Avanzados del IPN, Mexico show / hide abstract We present the growth and characterization of SmFeAsO1-xFx and NdFeAsO1-xFx thin films which have been grown by a two-step method: metalorganic chemical vapor deposition and a postannealing diffusion processes. Precursor films containing a mixture of Sm and Fe or Nd and Fe oxides were deposited on LaAlO3 substrates by MOCVD, using as starting precursors: SamariumTris(2,2,6,6-tetramethyl-3,5-heptanedionato), NeodymiumTris(2,2,6,6-tetramethyl-3,5-heptanedionato) and Iron(III) 2,4-pentanedionate. Afterwards, the arsenic and fluorine are incorporated during an annealing of these precursor films in presence of a SmFeAsO0.75F0.25 or NdFeAsO0.75F0.25 pellets. The results of the composition, evaluated by an energy dispersive X-ray analysis probe (EDX), and results of crystallographic evolution, obtained by X-ray diffraction indicate that the method is suitable for the development of the SmFeAsO1-xFx and NdFeAsO1-xFx phases with the P4/nmm crystalline structure. The secondary ion mass spectroscopy indicates a successful uniform diffusion process of both fluorine and arsenic ions through all the film thickness. The resistance and magnetic measurements as a function of the temperature indicate that the SmFeAsO1-xFx films present a superconducting transition, with a Tc that depends on the preparation conditions; nevertheless, the NdFeAsO1-xFx films did not show a superconducting transition at all. We discuss such different behavior based on the incorporation of fluorine and the presence of spurious phases. These results show that our thin films have good quality and, the most important, that the two-step method reported in this work is an alternative technique to MBE or PLD to obtain pnictides- superconducting films. This work was supported by the 163128 and 239895 projects of the CONACYT-México. |
Critical current density and vortex dynamics in Fe(Te,Se) annealed in various atmosphere TAMEGAI Tsuyoshi1, SUN Yue1, YAMADA Tatsuhiro1, TAEN Toshihiro1, PYON Sunseng1 1The University of Tokyo, Japan show / hide abstract Fe(Te,Se) has the simplest crystal structure among all iron-based superconductors. In addition, it only contains less toxic chalcogens rather than arsenic, and has attracted interest both from basic science and application point of view. It is also known that as-grown crystals of Fe(Te,Se) do not show bulk superconductivity and post-annealing in O2 [1], chalcogen [2,3], or pnictogen atmosphere [4] is necessary to induce bulk superconductivity. These annealing processes are believed to be effective in removing excess irons [5], which are harmful to superconductivity. We have characterized the value, distribution, and anisotropy of critical current density in the annealed Fe(Te,Se), and found that it is large, homogeneous, and isotropic [6,7]. We have also measured magnetic relaxation in the annealed Fe(Te,Se), and characterized vortex dynamics and vortex pinning mechanism [8]. We have also characterized some of normal state properties of well-annealed Fe(Te,Se). [1] Y. Sun, T. Taen, Y. Tsuchiya, Z. X. Shi, and T. Tamegai, Supercond. Sci. Technol. 26, 015015 (2013). [2] Y. Sun, Y. Tsuchiya, T. Yamada, T. Taen, S. Pyon, Z. X. Shi, and T. Tamegai, J. Phys. Soc. Jpn. 82, 093705 (2013). [3] Y. Sun, Y. Tsuchiya, T. Yamada, T. Taen, S. Pyon, Z. X. Shi, and T. Tamegai, J. Phys. Soc. Jpn. 82, 115002 (2013). [4] W. Zhou, Y. Sun, S. Zhang, J. C. Zhuang, F. Yuan, X. Li, Z. X. Shi, T. Yamada, Y. Tsuchiya, and T. Tamegai, J. Phys. Soc. Jpn. 83, 065001 (2014). [5] Y. Sun, Y. Tsuchiya, T. Taen, T. Yamada, S. Pyon, A. Sugimoto, T. Ekino, Z. X. Shi, and T. Tamegai, Sci. Rep. 4, 4585 (2014). [6] Y. Sun, T. Taen, Y. Tsuchiya, Q. P. Ding, S. Pyon, Z. X. Shi, and T. Tamegai, Appl. Phys. Express 6, 043101 (2013). [7] Y. Sun, T. Taen, T. Yamada, Y. Tsuchiya, S. Pyon, and T. Tamegai, Supercond. Sci. Technol. 28, 044002 (2015). [8] Y. Sun, T. Taen, Y. Tsuchiya, S. Pyon, Z. X. Shi, and T. Tamegai, Europhys. Lett. 103, 57013 (2013). |
Influence of substrate type on transport properties of superconducting FeSe0.5Te0.5 thin films YUAN Feifei1, IIDA Kazumasa2, LANGER Marco3, HÄNISCH Jens3, SHI Zhixiang4, SCHULTZ Ludwig1, HÜHNE Ruben1 1IFW Dresden, Germany, 2Nagoya University, Japan, 3Karlsruhe Institute of Technology (KIT), Germany, 4Southeast University, China show / hide abstract FeSe0.5Te0.5 thin films by pulsed laser deposition on CaF2, LaAlO3 and MgO substrates and structurally and electro-magnetically characterized in order to study the influence of the substrate on their transport properties. The in-plane lattice mismatch between FeSe0.5Te0.5 bulk and the substrates shows no influence on the lattice parameters of the films, whereas the type of substrates affects the crystalline quality of the films and, therefore, the superconducting properties. An extra peak in the angular dependence of critical current density Jc(θ) at θ= 180°(H||c) were showed for the film on MgO, which arises from c-axis defects as comfirmed by transmission electron microscopy. In constrat, no Jc(θ) peaks for H||c were observed in films on CaF2 and LaAlO3. Jc(θ) can be scaled successfully for both films without c-axis correlated by the anisotropic Ginzburg-Landau (AGL) [1] approach with approprite anisotropy ratio γJ. The scaling parameter γJ decreases with decreasing temperature, which is different from what we observed in FeSe0.5Te0.5 film on Fe-buffered MgO substrates [2]. [1] G. Blatter et al., Physical Review 147, 295 (1966). [2] K. Iida et al., Physical Review Letters 87, 104510 (2013). Support of this work by the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement number 283141 (IRON-SEA) and Strategic International Collaborative Research Program (SICORP), Japan Science and Technology Agency. We think I. Mönch, J. Scheiter, A. Ichinose, I. Tsukada, A. Sala, M.Putti, M. Kühnel and U. Besold for help |
Effect of in-plain strain on the phase diagram of Ru-substituted BaFe2As2 epitaxial thin films LANGER Marco1, GRINENKO Vadim2, HÄNISCH Jens1, YUAN Feifei2, IIDA Kazumasa3, HOLZAPFEL Bernhard1, SCHULTZ Ludwig2, HÜHNE Ruben2 1Karlsruhe Institute of Technology (KIT), Germany, 2IFW Dresden, Germany, 3Nagoya University, Japan show / hide abstract The antiferromagnetic iron pnictide BaFe2As2 exhibits superconductivity when the long-range spin density wave (SDW) order is sufficiently suppressed either by carrier doping, isovalent substitution (e.g. Ru) or external pressure. The phase diagram of Ba(Fe1-xRux)2As2 shows a superconducting dome up to an unusually high value of x ~ 40% in contrast to other substitution elements on the Fe-site [1]. In the last years, several explanations for the superconductivity in this system have been proposed, involving magnetic dilution, weakening of electronic correlations and the introduction of charge carriers in spite the fact that Ru is isovalent to Fe. Wang et al. tried to settle this debate by focusing their theoretical study on the effect of disorder introduced by Ru-substitution on the electronic structure and found a surprising insensitivity to the impurity scattering. Additionally, they found a reduction in the density of states at the Fermi level upon Ru-substitution [2]. Recently, we discovered that a tensile in-plain strain can induce superconductivity in undoped BaFe2As2 epitaxial thin films [3]. We also observed similarities between structural changes caused by Ru substitution and in-plain strain. Therefore, it is important to investigate the effect of in-plain strain on the phase diagram of Ru-substituted BaFe2As2 thin films. It is possible to introduce different amount of in-plane strain to the thin films using various single crystal substrates. It was found that the strain strongly affects both superconducting and antiferromagnetic SDW phases, revealing a strong structural dependence of the electronic properties. The results are discussed in comparison to data obtained on single crystals. [1] F. Rullier-Albenque et al., Phys. Rev. B 81, 224503 (2010) [2] L. Wang et al., Phys. Rev. Lett. 110, 037001 (2013) [3] J. Engelmann et al., Nat. Commun. 4, 2877 (2013) Support of this work by the German Research Foundation (DFG) within the framework of the Research Training Group 1621 and from European Union`s Seventh Framework Programme under grant number 283204 (Super-Iron) is gratefully acknowledged. M. Langer thanks J. Scheiter for technical assistance and J. Engelmann for fruitful discussions. |
Fabrication and characterization of the trilayers system Fe(Se,Te)/Fe/Fe(Se,Te) on Fe-buffered MgO and MgAl2O4 by pulsed laser deposition RODRIGUEZ Oscar1, MARIÑO Alvaro1, MOLATTA Sebastian2, HÜHNE Ruben2, HÄNISCH Jens3, HOLZAPFEL Bernhard2 1Universidad Nacional de Colombia, Colombia, 2Leibniz Institute for Solid State and Materials Research, Germany, 3Karlsruhe Institute of Technology (KIT), Germany show / hide abstract Superconducting multilayers are of great interest for fundamental research and electronic applications. One of the most interesting architectures, involves the superconductor/ferromagnet/superconductor systems (SFS) for the study of characteristics like the order parameter symmetry or the electrical properties of this type of Josephson juctions. Only a few works have been reported on the fabrication of pnictide superconducting multilayers. Given this, in this work we report an approach to the fabrication and characterization of a trilayer system SFS of Fe(Se,Te)/Fe/Fe(Se,Te). As a first step we deposited trilayers of Fe(Se,Te)/Fe/Fe(Se,Te) on Fe-buffered MgO and MgAl2O4 by Pulsed Laser Deposition (PLD). The trilayers grow c-axis oriented and biaxially textured, as θ-2θ scans and texture measurements revealed. This find, was confirmed by in-situ RHEED measurements where both superconducting layers present good crystalline properties. They show a superconducting transition of 11.1 K on MgO and 13.1 K on MgAl2O4. This is slightly lower than a single layer of Fe(Se,Te) on the respective templates. Oscar Rodríguez acknowledges to Colciencias for the scholarship support provided through its National Doctoral Program. We thank Michael Kühnel for technical support as well as Sabine Wurmehl and Michael Schulze for the provision of the FeSe0.5Te0.5 target. This work ws supported in part by the European Commision under project SUPERIRON grant 283204 |
1A-M-P-03 Sep 7 - Afternoon (2:00-4:00 PM) Materials - BSCCO, LTS, others I |
Ultrathin NbN Films on Flexible and Thickness Controllable Substrates JIA Xiaoqing1, LIANG Lanju1, JIN Biaobing1, WANG Zhihe1, HUANG Yi1, KANG Lin1, XU Weiwei1, CHEN Jian1, WU Peiheng1 1Nanjing University, China show / hide abstract A method for preparing superconducting NbN thin films on thickness controllable and flexible substrates has been developed, which is spin-coating polyimide on Si substrates, sputtering NbN films in room temperature and peeling-off substrates by wet etching technique. The superconducting NbN film with flexible polyimide substrate has been studied by XRD, AFM and PPMS. Zero resistance superconducting transition temperature (TC0) of these 10 nm thick films is 8.3 K and TC0 of 30 nm thick films in 9 tesla magnetic fields is still 7 K. This film can be utilized for multilayer terahertz metamaterial device, magnetic cloak and magnetic shielding. This work was supported by the National Basic Research Program of China (973 Program) Grants 2011CBA00107, 2011CBA00202 and 2014CB339804, the National Natural Science Foundation of China (NSFC) Grants 11227904 and 61101010. |
CARRIER LOCALIZATION, ANDERSON TRANSITIONS AND STRIPE FORMATION IN HOLE-DOPED CUPRATES KHUDAYBERDIEV Zafar1 1Institute of Nuclear Physics Academy of Sciences of Uzbekistan, Uzbekistan show / hide abstract In this work, we study theoretically possible mechanisms of carrier localization, metal–insulator transitions (MITs) and stripe formation in hole-doped cuprates. Three distinctly different scenarios are proposed for the carrier localization in three-dimensional (3D) lightly doped cuprates. The binding energies and radii of the extrinsic and intrinsic large (bi)polarons in cuprates are calculated variationally using the continuum model and adiabatic approximation. We have shown that the extrinsic and intrinsic 3D large bipolarons exist in lightly doped cuprates at η = ε∞/ε0 < 0.127 and η < 0.138, respectively, where ε∞(ε0) is the optic (static) dielectric constant. While the optical bipolarons can exist if η < 0.134 and the Fröhlich coupling constants α are greater than 5.8. The dopant- and carrier-driven inhomogeneities favor the specific charge ordering in the form of a 3D network of carrier-rich and carrier-poor stripes and the formation of different superlattices and in-gap bands of dopants and large polarons. The localized in-gap states develop into metallic states at some critical doping levels. We use the uncertainty relation to obtain the specific conditions for the Anderson and new MITs in cuprates. The applicability limits of these MITs in cuprates are clarified. We argue that the new MITs in the cuprates caused by the strong carrier–defect–phonon and carrier–phonon interactions are accompanied by the formation of a 3D self-organized network of carrier-poor (insulating) and carrier-rich (metallic) stripes, which coexist in a wide range of doping x ≈ 0.02-0.20, and the suppression of superconductivity observed in underdoped region near the x = 1/8 is caused by the formation of insulating stripes on a global scale and by the preponderance of insulating phase compared with the metallic one. Our results are in good agreement with the existing experiments on La-based and other cuprates. |
Influence of poly(vinyl alcohol) on superconducting properties of Hg-1223 HTS METSKHVARISHVILI Ioseb1, DGEBUADZE G.1, LOBZHANIDZE T.2, BENDELIANI B.1, METSKHVARISHVILI M.3, GABUNIA V.1 1I. Vekua Sukhumi Institute of Physics & Technology, Georgia, 2Ivane Javakhishvili Tbilisi State University, Georgia, 3Georgian Technical University, Georgia show / hide abstract The HgBa2Ca2Cu3O8+δ high temperature superconductor shows superconducting transition temperature Tc above 135 K and Tc≈165K under the external pressure. These characteristics make the Hg-1223 phase a very attractive material for producing superconducting wires, tapes, and thin-films. Therefore, creation simpler and reliable technologies for synthesized high stability Hg-1223 phase are very important subjects in order to achieve the large-scale technological applications of mercury-based superconductors. We report the wet chemistry methods for preparation Hg-based polycrystalline superconductors. For synthesized Hg-1223 samples, we used two-step method. In the first stage non-mercury containing precursor was prepared before proceeding to the second stage where HgO was added to the precursor before final sintering. The synthesis of Ba2Ca2Cu3Oy is carried out by dissolving separately CaCO3 in acetic acid, CuO in ammonium chloride and BaCO3 in distilled water. The solutions are mixed afterward in the stoichiometric ratio. To this solution were added poly(vinyl alcohol) (PVA). The solution dried at 180oC temperature for 12 h and after obtained gel was dreaded at 300oC. The xerogels are then homogenised in an agate mortar and calcined at 750oC, during 4 h in a muffled furnace. The obtained precursor is then mixed with HgO in nominal stoichiometric quantity. The resulting powder is pelletized and inserted in a quartz tube that is closed under vacuum. These pellets were sintered in furnace at 800oC for 6 hours. The structure of the obtained materials was determined by XRD. Transition temperature was measured by ac susceptibility and critical currents density Jc by high harmonic methods. Finally, including poly(vinyl alcohol) in preparation precursor Ba2Ca2Cu3Oy we observed single-phase and purity high temperature Hg-1223 phase. This work has been fulfilled by financial support of the Shota Rustaveli National Science Foundation, Grant No. FR/423/6-260/12. |
Thin films and multilayers of Nb3Sn for high-field RF applications SUNDAHL Christopher1, SOSA Salvador2, EREMEEV Grigory3, DELAYEN Jean2, GUREVICH Alexander2, EOM Chang-Beom1 1University of Wisconsin-Madison, United States, 2Old Dominion University, United States, 3Thomas Jefferson National Accelerator Facility, United States show / hide abstract Nb3Sn is one of the widely used practical superconductors for dc high field magnet applications. There is also much interest in using Nb3Sn for radio-frequency (RF) applications, particularly in superconducting resonator cavities for particle accelerators [1]. However, the small lower critical field Hc1 limits the ability of Nb3Sn to withstand high RF fields > 100 mT as penetration of vortices causes strong dissipation. To address this problem it was suggested to coat the Nb resonator cavities with superconductor-Insulator-Superconductor (SIS) multilayers in which the thickness of Nb3Sn films is smaller than the London penetration depth [2]. In this work we have grown and tested thin films and multilayers of Nb3Sn and dielectrics on oxide substrates. These structures have been fabricated by two different approaches: first, by the alternating deposition of Nb and Sn layers followed by annealing; and second, by co-deposition of Nb and Sn at high temperature. Temperature dependencies of the low-field quality factor were measured at 7.4 GHz for 50 and 100 nm thick Nb3Sn bilayers. The Nb3Sn films have shown good screening properties and the onset of superconductivity close to the bulk Tc. SIS multilayers were also fabricated and tested for their RF properties. The results were compared to previous studies conducted on SIS multilayers of other materials such as NbN [3]. [1]. S.M. Deambrosis, G. Keppel, V. Ramazzo, C. Roncaloto, R.G. Sharma, and V. Palmieri, Physica C 441 (2006) 108. [2]. A. Gurevich, Appl. Phys. Lett. 88 (2006) 012511. [3]. C. Z. Antoine, J. C. Villegier, and G. Martinet, Appl. Phys. Lett. 102 (2013) 102603. Work supported by the US Department of Energy under grant No. DE-SC0010081. |
Preparation of Bi-2223 thick films on silver substrates by dip-coating method DENG Shutong1, QU Timing1, LIN Guan1, HAN Zhenghe1 1Tsinghua University, China show / hide abstract In this study, the high temperature superconductor (Bi,Pb)2Sr2Ca2Cu3Ox (Bi-2223) thick films were fabricated by dip-coating method on silver substrates. Two deposited precursor films were stacked “Face-to-face” (FTF) to prevent the volatilization of specific elements during sintering. Two-step heat treatment was studied. The sintering temperature was fixed on 835 oC and different sintering time was investigated in an 8.5% O2 (N2 balanced) for the first period heat treatment (HT1). After pressed by 1.0 GPa, the samples were sintered at 825 oC in an 8.5% O2 (N2 balanced) for the second heat treatment (HT2). The thick film which was sintered for 10 h in HT1 showed a zero-resistance transition temperature (TC0) of 107.9 K and a critical current density (JC) of 1100 A/cm2 (77 K, 0 T). And its JC value was 5500 A/cm2 (77 K, 0 T) after HT2. The authors own great thankfulness for the support from the National Natural Science Foundation of China (51475257), the Development Foundation of Shenzhen (JCYJ20130402145002389), and the Tribology Science Fund of State Key Laboratory of Tribology, China. |
Fabrication of (Bi,Pb)2Sr2Ca2Cu3Ox superconducting thin film on LAO substrate by using chemical solution deposition method LIN Guan1, QU Timing1, DENG Shutong1, GU Chen1, HAN Zhenghe1 1Tsinghua University, China show / hide abstract In this study, textured (Bi,Pb)2Sr2Ca2Cu3Ox ((Bi,Pb)-2223) thin films were successfully fabricated on LaAlO3 (100) substrates by using chemical solution deposition (CSD) method. The precursor solution was produced from acetates and nitrites dissolved in acetic acid and ammonia water. The as prepared solution was spin-coated on LAO substrates. The heat treatment includes a pyrolysis process at 500 oC and a sintering process at above 800 oC in reduced oxygen atmosphere. The growth of pure (Bi,Pb)-2223 phase through CSD is quite challenging due to the volatilization of specific elements during high temperature heat treatments. This element loss can be reduced by sealing the pyrolyzed films inside a silver foil with (Bi,Pb)-2223 precursor powder surrounded. Films with the thickness of about 150 nm were obtained after sintering. The microstructures and superconducting properties were investigated. It is shown from the X-ray diffraction patterns that the content of (Bi,Pb)-2223 phase varied with increasing sintering temperature, with the maximum value achieved at 845 oC. Strong bi-axial texture was also observed. The critical temperature for all samples is around 104 K. The critical current density for the optimized sample reached more than 0.05 MA/cm2 at 77K. The authors own great thankfulness for the support from the National Natural Science Foundation of China (51475257), the Development Foundation of Shenzhen (JCYJ20130402145002389), and the Tribology Science Fund of State Key Laboratory of Tribology, China |
Effect of Pressing on Structural, Mechanical and Superconducting Properties of BSCCO Bulk Materials SAFRAN Serap1, KILIC Ahmet1, ASIKUZUN Elif2, OZTURK Ozgur2 1Ankara University, Turkey, 2Kastamonu University, Turkey show / hide abstract The superconducting, structural and mechanical properties of BSCCO bulk samples have been studied as a function of pressure by means of AC susceptibility, XRD and microhardness measurements, respectively. In this study, 3 samples have been prepared. All samples are kept for 120 h at 845 οC and then cooled by 1 οC/min rates from annealing temperature to 200 οC in air atmosphere. During the preparation of the samples one and two intermediate pressed are applied at 75MPa. X-ray diffraction analysis shows that both Bi-2223 and Bi-2212 phases detect for all samples. However, according to intermediate pressing, Bi-2223 phases getting higher. The critical transition temperature, phase purity and crystallinity of the prepared bulk samples are compared with each other. Elasticity (E), brittleness (Bi), fracture toughness (KIC) and yield strength (Y) values are also determined according to annealing time, applied load and production parameters of materials. This work has been supported by Turkish Research and Scientific Council (TUBITAK) under grant contract No: 113F150. We also acknowledge The Republic of Turkey, Ministry of Development under the Project Number 2010K120520. |
A proximity effect in the HTS/Ferromagnet multilayers as the probing method of symmetry of superconducting order parameter in HTS compounds KHUSAINOV Mansur1, KHUSAINOV Marat1, SAKHRATOV Yuriy2, MATUKHIN Vadim2, PROSHIN Yurii1 1Kazan Federal University, Russia, 2Kazan State Power Engineering University, Russia show / hide abstract The proximity effect is theoretically studied for thin and bulk pure HTS/F contacts, where F is a ferromagnet and HTS is a high-temperature superconductor. It is shown that there is no continuous matching between the s-wave and d-wave pair amplitudes at the HTS/F boundary. In thin HTS/F nanostructures the exchange field strongly suppresses the averaged s- and d-pairing and leads to the competition between Bardeen-Cooper-Schrieffer (BCS) and Fulde-Ferrell-Larkin-Ovchinnikov scenarios of superconductivity. On the contrary, in bulk HTS/F contact the exchange field has no effect on the critical temperature Tcd of d-wave pairing. This is due to the lack of d-wave pairing in F layers, resulting in full internal reflection of d-wave pairs even from perfectly transparent HTS/F boundary. The s-wave superconductivity localized at the HTS/F interface is predicted. Due to a strong damping of the surface critical temperature Tcd for the d-wave component, one should expect spontaneous symmetry change of the order parameter at the HTS/F interfaces from initially d-wave type to s-type, because Tcs of the s-wave component is proved to be higher than Tcd. It qualitatively agrees with experimental observation of the mixture of s- and d- wave components at the Ag/BiSrCaCuO and Fe/Ag/BiSrCaCuO interfaces [1,2]. Moreover, many of HTS experts suppose, that the spin-fluctuation mechanism in HTS is realized, leading to the d-wave symmetry of superconducting order parameter. On the other hand, K.A. Müller, discoverer of HTS systems, considers that the d-wave symmetry of the order parameter is realized on the surface of HTS while the BCS mechanism with s-wave pairing is implemented in the bulk [3]. We believe, that the problem of the symmetry of the HTS order parameter could be studied based on the proximity effect in HTS/F and HTS/S nanostructures, if conventional BCS superconductor (S) or ferromagnet is used as a peculiar kind of probe (see [4] for F/S systems). 1. M. Freamat, K.-W. Ng, Phys. Rev. B 68, 060507 (2003) 2. K.-W. Ng, M. Freamat, Int. Journ. Mod. Phys. B 19, 495 (2005) 3. K.A. Müller, Physica C 387, 57 (2003) 4. M.G. Khusainov, et al., JETP Lett. 89, 626 (2009); ibid. 90, 124 (2009) The work is partially supported by Russian Government Program of Competitive Growth of Kazan Federal University. Marat Khusainov is also thankful to the RFBR (13-02-01202) for partial support. |
Growths and interfacial properties of sputter-deposited NbN films ZHANG Yu1, WANG Sansheng1, LI Minghui1, HU Yanting2, GUO Qiang1 1Beihang University, China, 2University of Jinan, China show / hide abstract Growths and interfacial properties of NbN films deposited on MgO substrates by magnetron sputtering were investigated. The epitaxial NbN Films can be deposited on the MgO substrates. However, the interface effect between film and substrate is often reported to be strongly defective due to lattice mismatch, so that the conductivity of NbN films gets worse. In this paper, we investigate the transport properties and crystal structures of NbN films on different crystal oritentation MgO sunstrates. Meanwhile, we also investigate the relationships between the growth parameters including growrh temperature, growth atmosphere, substrate pretreatment and superconductivity of NbN films. Moreover, the surface structures of films and substrates are also investigated by Low energy diffraction (LEED) and high energy electron diffraction (RHEED). This work was supported by 863 project of china (No.2014AA032703) and The National Natural Science Fund of china (No.61171003) and CAST-BISEE innovation fund of Beijing Institute of Spacecraft Environment Engineering. |
Magnetic and electrical properties of a single weak-link in a Nb film carved with focused ion bean VALERIO CUADROS Marlon1, MOTTA Maycon1, COLAUTO Fabiano1, MENDONÇA DE OLIVEIRA Ana2, HELGUEIRA DE ANDRADE Antonio3, HENNING JOHANSEN Tom4, AIRES ORTIZ Wilson1 1Universidade Federal de São Carlos, Brazil, 2Instituto de Federal de Educação, Ciência e Tecnologia, Brazil, 3Instituto de Física, Universidade Federal do Rio Grande do Sul, Brazil, 4Department of Physics, University of Oslo, Norway show / hide abstract Granular superconductivity occurs when microscopic superconducting grains are connected with neighbors either by non-superconducting materials, or by less robust superconductors, or even by a physical constriction, i.e., an equally strong superconductor of smaller cross section. The intragranular component is related to the essence of the grains, governed by the inherent properties of the material while, on the other hand, the intergranular part is associated with grain boundaries coupling neighboring grains - the so-called weak-link. One characteristic feature of granular superconductors is the occurrence of a double resistive superconducting transition and the typical two-peaks and two-plateaus in the ac-susceptibility components. Using ac-susceptibility and magneto-transport measurements, we have investigated the superconducting properties of weak-links created artificially in Nb films. The 200 nm thick Nb thin films with rectangular shape (3 x 1 mm2), were deposited by magnetron sputtering in a UHV system. A Focused Ion Beam apparatus was employed to carve a groove in the central region of the film, along its width, creating thus two identical grains. The groove, which acts as a single weak-link, had its depth and width controlled by the FIB dose. The topographical characterization was performed by use of atomic force microscopy. Magnetic and magneto-transport measurements, as well as magneto-optical imaging, were used to determine the superconducting parameters associated with the grains and with the weak-link. |
Ambient temperature growth of mono- and polycrystalline NbN nanofilms and their surface and composition analysis KRAUSE Sascha1, AFANAS'EV Victor2, DESMARIS Vincent1, MELEDIN Denis1, PAVOLOTSKY Alexey1, BELITSKY Victor1, LUBENSCHENKO Alexander2, BATRAKOV Alexander2, RUDZINSKI Mariusz3, PIPPEL Eckhard4 1Chalmers University of Technology, Sweden, 2National Research University "MPEI", Russia, 3Institute of Electronic Materials Technology (ITME), Poland, 4Max-Planck-Institut für Mikrostrukturphysik, Germany show / hide abstract This paper reflects on the investigation of high-quality 5nm thin NbN films deposited by means of reactive DC magnetron sputtering at room temperature. The deposition without intentional substrate heating offers major advantages from a processing point of view and motivates the extensive composition- and surface characterization and comparison of present films with high quality films grown at elevated temperatures. Monocrystalline NbN films have been epitaxially grown onto hexagonal GaN buffer-layers (0002) and show a distinct, low defect interface as confirmed from High-Resolution TEM. The critical temperature (Tc) of those films reached 10.4K. Furthermore, a poly-crystalline structure was observed on films grown onto Si (100) substrates, exhibiting a Tc of 8.1K albeit a narrow transition from the normal to the superconducting state. X-ray photoelectron spectroscopy and reflected electron energy loss spectroscopy verified that the composition of NbN did not differ irrespectively of applied substrate heating. Moreover, the native oxide layer at the surface of NbN has been identified as NbO2 and thus, is in contrast to the Nb2O5, usually being formed at the surface of Nb when exposed to air. These findings are of significance since it was proven the possibility of growing epitaxial NbN onto GaN buffer layer in the absence of high temperatures hence paving the way to employ NbN in more advanced fabrication processes involving a higher degree of complexity. The eased integration and employment of lift-off techniques could, in particular, lead to improved performance of cryogenic ultra-sensitive terahertz electronics. |
Orientation Engineering for the Growth of c-axis and Non-c-axis Epitaxial Bi2Sr2CaCu2O8+δ Thin Films by MOCVD ENDO Kazuhiro1, ARISAWA Shunichi2, KANEKO Toshiyuki1, TSUYUMOTO Isao1, TATENO Yasushi1, YAMASAKI Hirofumi3, BADICA Petre4 1Kanazawa Institute of Technology, Japan, 2National Institute for Material Science, Japan, 3National Institute of Advanced Industrial Science and Technology, Japan, 4National Institute of Materials Physics, Romania show / hide abstract Materials may show anisotropic properties on different crystal directions and this is also the case of High Temperature Superconductors (HTS). To take advantage of the materials anisotropy one concept of interest is "orientation engineering" in thin films. This can be realized through the control of the film-substrate lattice relationships. We prepared c-axis oriented films of Bi2Sr2CaCu2O8+δ (Bi-2212) superconductor on SrTiO3 (001) and LaAlO3 (001) substrates, and non-c-axis oriented films of Bi-2212 superconductor on SrTiO3 (110) and LaAlO3 (110) substrates by metalorganic chemical vapor deposition (MOCVD). These substrates were selected from the view point of lattice misfit between film and substrate. Improved non-c-axis oriented films with single phase of Bi-2212 were obtained by two-temperatures template method on SrTiO3 (110) and LaAlO3 (110) substrates. These c-axis and non-c-axis orientations were examined by X-ray diffraction (XRD) method with θ-2θ scans and φ-ψ scans. Superconducting properties and surface morphology of obtained films were evaluated by four-probe resistivity measurement, scanning electron microscopy (SEM), and atomic force microscopy (AFM). It is expected that in the future "orientation engineering" will generate new nano composite materials with new properties and effects leading to development of new devices with new or improved functionality. |
1A-M-P-04 Sep 7 - Afternoon (2:00-4:00 PM) Materials - YBCO films |
A method to fabricate bi-axially textured MgO buffer layer for HTS coated conductor XIAO Shaozhu1, FENG Feng2, QU Timing3, HAN Zhenghe1 1Applied Superconductivity Research Center, China, 2Division of Advanced Manufacturing, China, 3Department of Mechanical Engineering, China show / hide abstract In the deposition of MgO films by radio frequency magnetron sputtering method, the growing film is usually bombarded by energetic particles mainly composed of oxygen atoms and negative oxygen ions with energy of several hundred eV. The bombardment could cause reduction in the film thickness , which is usually called re-sputtering effect. In this study, the density distribution of energetic particles was obtained from the thickness profile of as-deposited MgO film. It was found that the energetic particle flux was well collimated. Thus, a new method was designed to fabricate bi-axially textured MgO buffer layer using the energetic particle flux. In the deposition area simultaneously bombarded by energetic particles from 55° tilted target, MgO layer could develop bi-axial texture within 10 nm thickness on the substrate of amorphous Y2O3 buffered Hastelloy C276. The XRD measurement indicated that the MgO layer exhibited a (111) out-of-plane orientation and a 3-fold symmetric in-plane orientation. This method performed similar to the ion beam assisted deposition (IBAD) method but didn’t need any ion sources. The influence of sputtering parameters, such as duration of deposition and so on, on the bi-axial texture of MgO was investigated. This study was supported by National Natural Science Foundation of China (51402165), Guangdong Natural Science Foundation (S2013040014199), and Fundamental Research Program of Shenzhen (JCYJ20140827160129762). |
Jc enhancement by LAO doping in YBCO films both in self-field and magnetic field XU Yan1, SUO Hongli1, ZHAO Yue2, GRIVEL Jean2, LIU Min1 1Beijing University of Technology, China, 2Technical University of Denmark, Denmark show / hide abstract To enhance the Jc of YBCO films both in self-field and under magnetic field, an effective strategy is to introduce artificial pining centers and keep a good YBCO matrix at the same time. Here we propose a new dopant ---LaAlO3 (LAO), based on its chemical stability and small mismatch towards YBCO. A series YBCO films with different LAO doping contents were fabricated on LAO single crystal substrates by metal organic deposition. We observed that though a lot of LAO is added to YBCO, by XRD measurement and SEM observations YBCO still keep a good epitaxial growth relationship. Superconductivity is investigated by VSM, and an unusual curve of moment loop is found at low temperature. There is a moment peak appoximately at -0.01T and +0.01T respectively and a result is that the highest Jc is obtained at 0.01T. Besides, the improvement observed under magnetic field, the Jc of the doped sample also is significantly enhanced in self-field compared to a pure YBCO film. The Jc of the 5% LAO doped sample is enhanced more than 3times in self-field 77K, whereas at 77K and 1.5T, the Jc value is 7 times larger than in the pure YBCO film. These results indicate that LAO doping can effectively enhance the Jc of YBCO films both in self-field and in applied magnetic fields. This work is financially supported by the Chnia Scholarship, National Natural Science Foundation of China(51171002), the Project of Construction of Innovative Teams and Teacher Career Development for Universities and Colleges Under Beijing Municipality(IDHT20130510), and by 211 Program of Beijing City |
Aging of Precursor Solutions Used For YBCO Films Chemical Solution Deposition: Study of Mechanisms and Effects on Film Properties PINTO Valentina1, ANGRISANI ARMENIO Achille1, MANCINI Antonella1, RIZZO Francesco1, VANNOZZI Angelo1, RUFOLONI Alessandro1, AUGIERI Andrea1, GALLUZZI Valentina1, SOTGIU Giovanni2, SILVA Enrico2, SANTONI Antonino1, FLAMINIA Rondino1, FABBRI Fabio1, LAMANNA Raffaele1, CELENTANO Giuseppe1 1ENEA, Italy, 2RomaTre University, Italy show / hide abstract The proposed study investigates the aging of two precursor solutions used for chemical solution deposition (CSD) of YBa2Cu3O7-x (YBCO) and composite YBCO films with nanostructured inclusions of BaZrO3 (YBCO-BZO). The stability of precursor solutions plays a crucial role to determine the crystalline quality and the superconducting properties of YBCO films. Even though low or free fluorine solutions are promising in order to improve the synthesis route and to reduce the environmental impact, the poor stability of the solution is the major drawback of the low-fluorine precursors, since they degrade faster (4-6 weeks) than other precursor solutions for superconducting layers (e.g. trifluoroacetates solutions are stable up to 6 months) or buffer layers (stable for several months). Therefore, a deeper comprehension of the degradation mechanisms is fundamental to properly optimize the precursor solution composition. The current work studies two precursor solutions (for YBCO and YBCO-BZO) that are complex systems in which different interactions need to be considered: most of all, the nature of ligands (acetate, propionate, ammonia) that complex each metal and influence not only the solution stability but also the quality of the deposited film. Thus, information obtained from different analyses [Fourier transformed infrared spectroscopy (FT-IR), thermal analyses (DTA/TG) coupled with mass spectrometry (MS), X-ray photoelectron spectroscopy (XPS), Raman Spectroscopy, Nuclear Magnetic Resonance (NMR)] is correlated with morphological, structural and superconducting properties of the deposited film in order to understand the underlying chemical mechanisms of aging (salts precipitation, oxidation, polymerization,..) and its effects. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. |
Study on The Field Properties and Pinning mechanism of YBCO Superconducting Film with Nb Doping LIU Min1 1Beijing University of Technology, China show / hide abstract YBCO/BYNO nano-composite was successfully fabricated by metal organic deposition method based on trifluoroeacetate salts (TFA-MOD). The paper systematically studied the influence on the microstructure, surface quality and on the superconducting properties of the YBCO films with different content of Nb dopant. It is demonstrated that the microstructure of YBCO films had not an obvious impact for a Nb doping amount of less than 10mol.%, while the surface quality of YBCO is still improved. Although the critical transition temperature (Tc) of YBCO decreased slightly after Nb doping, it was kept as high as 90K for the present experiments. In addition, a significant enhancement of the critical current density (Jc) was observed for YBCO films with BYNO nanoparticles compared to those of pure YBCO films both in self-field and applied field. The epitaxial and random oriented BYNO nanoparticles coexisted in YBCO nanocomposites, which can be explained by the nucleation model. The size of the BYNO is between 20nm and 30nm, while the random fraction of BYNO was above 90%. The stacking fault parallel to the film and a serious lattice distortion of YBCO can be found around the BYNO nanoparticles, which could strengthen the nanostrain in the nanocomposite. As increasing the random fraction of BYNO, the nanostrain within nanocomposites was strengthened. According to that, the enhancement of field properties of BYNO resulted from the enhanced nanostrain. The present results can provide the basis for the enhancement of the in-field properties of YBCO nanocomposite. |
Development of low fluorine solution for YBCO film growth JIN Lihua1, YU Zeming1, FENG Jianqing1, LI Chengshan1, WANG Yao1, ZHANG Pingxiang1 1Northwest Institute for Nonferrous Metal Research, China show / hide abstract The low fluorine solution was useful for the epitaxial growth of YBa2Cu3Oy (YBCO) film. In this paper, we developed a series of low fluorine solutions containing different content of fluorine to fabricate YBCO film on buffered NiW substrates and single crystal LaAlO3 substrates. In comparison with the traditional all TFA solution, these new low fluorine solutions had 0% - 50% of fluorine content. Fast pyrolysis process and smooth surface of YBCO precursor films could be acquired by using the low fluorine solution. The phase, texture, microstructure and superconducting properties of YBCO films were characterized by X-ray diffraction, scanning electron microscopy and four-probe method. When the optimal fluorine content was 23%, the solution could significantly reduce the formation of BaCO3 and increase the formation of BaF2 in the pyrolyzed film. The YBCO films with a critical current density (Jc) of ~ 2.6 MA/cm2 (77K, 0T) could be obtained on buffered NiW substrates (CeO2/YSZ/CeO2/NiW) from the low fluorine solution. This work was financially supported by the International Science & Technology Cooperation Program of China (No.2012DFA50780), the National Science Fund Program of China (No. 51302225 and 51202201), the Innovative Research Team of Shaanxi province (No.2013KCT-07), the Science & Technology Nova Program of Shaanxi Province (No.2014KJXX-23). |
SrTiO3 buffer layer grown at low temperature on reinforced cube-textured Cu-based substrate by PLD for YBCO Coated Conductor XURIGUERA Elena1, PADILLA Jose2, RODRÍGUEZ Laura2, VANNOZZI Angelo3, RUFOLONI Alessandro3, CELENTANO Giuseppe3 1La Farga Lacambra SAU, Spain, 2Universitat de Barcelona, Spain, 3ENEA, Italy show / hide abstract Strontium titanate (STO) is an ideal candidate to use as a single buffer layer for growing high quality YBa2Cu3O7-X (YBCO) film. Biaxially textured STO buffer layer has been grown by pulsed laser deposition (PLD) on rolling assisted biaxially textured substrates (RABiTS) made of low cost Cu-clad stainless steel substrate with textured electroplated Ni provided by Tanaka Kikinzoku, which exhibits a very strong cube texture and a roughness below 10 nm. This study presents the development and optimization of the maximum achievable thickness of highly textured (00l) STO films on metallic substrates by means of PLD process using reducing atmosphere (Ar/5%H2) to prevent the oxidation of the substrate. STO was deposited by PLD using excimer laser KrF at different temperatures from 300 to 850 ºC. Optimization of the parameters of PLD process shows that STO film deposited at 500 ºC exhibits the best quality texture with high repeatability. On the other hand, STO films were deposited with different thickness, i.e. 0.3, 0.5, 0.8 and 1 µm, to achieve the maximum thickness with the best texture and quality surface. XRD analyses reveal an excellent quality of biaxial texture and SEM images show an adequate two dimensional growth of the layer and a smooth surface, in all the cases. EBSD analyses are in line with XRD measurements from 0.3 to 0.8 µm and show that STO films grow epitaxially, with a fraction of oriented area exceeding 97% with 12º tolerance angle, whereas at 1 µm of thickness the surface texture is strongly deteriorated. The optimum thickness with the best texture quality is 0.8 µm of STO, with a rms roughness of about 5 nm and the full width at half maximum (FWHM) of omega-scans RD and TD of (002) STO and phi-scan (111) STO are 4.5º, 6.2º and 5.3º, respectively. STO/Ni/Cu-clad stainless steel architecture prepared by PLD under reducing atmosphere and low temperature may provide useful templates for the growth of YBCO coated conductors. The research leading to these results has received funding from the European Union’s Seventh Framework Programme (FP7/2007-2013) under grant agreement nº 280432. |
Superconducting Dy1-xGdxBa2Cu3O7-d thin films made by Chemical Solution Deposition OPATA Yuri1, WULFF Anders1, ZHAO Yue1, HANSEN Jørn1, GRIVEL Jean-Claude1 1Technical University of Denmark, Denmark show / hide abstract A series of Dy1-xGdxBa2Cu3O7- d (DGBCO) thin films, with partial substitution of Dy with Gd (with 0 ≤ x ≤ 0.2), was fabricated on LaAlO3 single crystal substrates by means of TFA-MOD, using trifluoroacetates. Thin film properties were investigated using Vibrating Sample Magnetometry, X-ray diffraction and Scanning Electron Microscopy. Analysis of X-ray diffraction patterns for all samples reveals that the (123)-phase is formed and minor reflections representing other phases are observed. The critical temperature was about 89 K and found to be independent of the substitution ratio between Dy and Gd. Analysis of critical current densities and pinning forces are also presented in this work. This work was supported by Capes agency - Proc. n° BEX 13491/13-0. Authors thanks the Department of Energy Conversion and Storage of Technical University of Denmark. |
Pyrolysis study of thick deposited YBCO precursor layers by ink jet printing VILLAREJO Bohores1, POP Cornelia1, RICART Susagna1, SORT Jordi2, FARJAS Jordi3, ROURA Pere3, OBRADORS Xavier1, PUIG Teresa1 1Institut de Ciència de Materials de Barcelona, Spain, 2Institució Catalana de Recerca i Estudis Avançats, Spain, 3GRMT, University of Girona, Spain show / hide abstract Chemical solution deposition (CSD) offers a versatile and low cost methodology for the production of coated conductors; however, reaching thick films by CSD becomes one of the main challenges for this technique due to the high stress produced during pyrolysis, which may lead to buckling and crack formation, so degraded superconducting properties. The pyrolysis study of low fluor metalorganic Y, Ba and Cu precursor solutions deposited by a single-nozzle inkjet printer (IJP) was carried out for gel deposited layers of several microns. The main investigated parameters were the effect of the heating rate and the solution formulation. Thermo gravimetric analysis (TGA), evolved gas analysis (EGA) and infrared spectroscopy (IR) were performed to study the evaporation/decomposition of organic products along pyrolysis. Thickness evolution was studied in different stages by profilometry and the mechanical properties of the gel by nanoindentation. In addition a new analytical tool was implemented (Pyrolyzer) based on a heating stage device coupled to an optical microscope that allows the recording of the whole process. First of all, we indentified the zone of maximum shrinkage before the decomposition of organic matter (T<280ºC), where also buckling may be reversible in certain cases. During this shrinkage zone, buckling and cracking may appear as stress relief mechanism which shows up clearly separated. Buckling formation was observed at rather low temperatures (~200ºC) associated to an elastic regime. Cracking, on the other hand, was identified as an irreversible phenomenon at higher temperatures (~270ºC), once the layer becomes stiffer. All this kinetic study has enabled us to optimize the overall pyrolysis process to obtain single deposited thick pyrolyzed films (~2 µm) with the homogeneous morphology required to obtain high performance, ~1 µm, YBCO epitaxial films Finally, we demonstrate that multideposition of these YBCO thick layers by inkjet printing is a successful and very promising approach to achieve film thickness beyond 1µm. Following the optimized pyrolysis process high quality thick films (> 1 µm) may be achieved. Acknowledgements. The research leading to these results has received funding from EU-FP7 NMP-LA-2012-280432 EUROTAPES project, MP1201 Cost action and MAT2014-51778-C2-1-R national project. |
Ultra-high speed pulsed laser deposition of YBCO layer in processing of long HTS coated conductors RUTT Alexander1, SCHNEIDER Thomas1, KIRCHHOFF Lutz1, HOFACKER Frank1, HESSLER Andreas1, SWISTUNOVA Olga2, USOSKIN Alexander1 1Bruker HTS, Germany, 2Kurchatov's Institute, Russia show / hide abstract Abnormal increase of deposition speed by pulsed laser deposition process (PLD) is investigated. Deposition speeds from 0.1 to 10 nm per elementary laser pulse were analysed regarding critical current in HTS coated conductors. Experiments were performed in PLD installation employed for deposition of both ceria cap buffer and YBCO layers. Cr-Ni stainless steel tape preliminary coated with bi-textured yttria-stabilized-zirconia buffer layer via alternating beam assisted deposition (ABAD) is used as a substrate. Perturbations of crystallinity in YBCO films were observed at highest deposition speeds. In spite of reduction of crystalline and morphology perfection only a moderate reduction of critical current in HTS films was found. Maxima in dependences of critical current versus deposition speed at different temperatures are demonstrated and discussed. Influence of tape tension during PLD process as well as initial substrate/buffer defects are shown to be a reason for dropouts in transport current across the tape length. Alternative possibilities for suppression of these defects are discussed. Effects of smoothening of local peculiarities in YBCO films with increased thickness are identified and reported. Feasibility of ultra-high speed PLD is analysed taking into account magnetic field strength under which operation of tape is expected. |
Effects of strontium substitution in YBa2Cu4O8 films by the KOH flux method MIYACHI Yugo1, FUNAKI Shuhei1, OKUNISHI Ryota1, YAMADA Yasuji1 1Shimane University, Japan show / hide abstract In order to reveal the origin of Tc increase of Sr-substituted YBa2Cu4O8 (Y124), we have fabricated Sr-doped Y124 crystals by KOH flux method, which can grow high quality single crystals. In the previous work done for powder crystals, we found that the Tc determined by magnetization measurement enhances as fabrication temperature decreases. In this study, in order to confirm the evidence of Tc increase by means of electrical resistivity measurement and investigate the correlation between Tc and lattice constant, we deposited Sr-doped Y124 films on NdGaO3 (001) substrates by the KOH flux method. Y2O3, BaCO3, SrCO3 and CuO were used for raw materials, and NdGaO3 (001) substrate was used for a seed crystal. Nominal composition was Y:Ba:Sr:Cu = 1:1.8:0.2:4 in molar ratio. 100 wt% KOH to the raw materials were used as a flux. The raw material powders and flux were hated up to 600-700ºC in an alumina crucible and kept for 12 hours. The fabrication of Y124 films were identified by XRD measurement. The film fabricated at 700ºC showed zero-resistance at 80 K (Tczero) and the c-axis length of 27.19 Å. In contrast, the film fabricated at 600ºC showed Tczero = 84.5 K and c = 27.24 Å, showing Tc enhancement. As is the case of powder crystals, Sr-doped Y124 film fabricated at a low temperature showed a higher Tc value than at a high temperature. Additionally, compared to film fabricated at 600ºC, the c-axis length of film fabricated at 700ºC contracted. Some reports dealing with Sr-substituted Y124 concluded that the Tc increases by lattice construction and chemical pressure effect by the incorporation of Sr to the Ba sites. This study indicates the opposite relationship between Tc enhancement and c-lattice contraction. Consequently, the origin of the improvement of Tc observed on the Sr-doped Y124 fabricated at low temperature by the KOH flux method is not chemical pressure effect but hole-dope effect by the incorporation of Sr2+ to the Y3+ sites. |
Process potential of KOH flux method for very low temperature growth of REBa2Cu3O7-δ crystal and film YAMADA Yasuji1, FUNAKI Shuhei1, OKUNISHI Ryota1, MIYACHI Yugo1 1Shimane University, Japan show / hide abstract Rare-earth based oxide superconductors REBa2Cu3O7-d (RE123: RE=rare-earth elements) and REBa2Cu4O8 (RE124) can be grown from the solution made of molten potassium hydroxide (KOH) at low temperatures around 500ºC. The low temperature growth using KOH flux is quite suitable for the production of RE123 films on various substrate materials. Since KOH flux growth is a near equilibrium process, RE123 and RE124 can be obtained depending on temperature and oxygen partial pressure (PO2). To find out the proper growth conditions of RE123 from KOH flux, temperature and PO2 dependence in phase formation was investigated. Superconducting property was also measured by SQUID magnetometer and transport measurement to find out whether there are some effects of KOH flux on RE123 superconductivity depending on temperature and PO2. As same as the phase relations reported for solid-state reaction process, Y123 phase was formed from KOH flux at a high temperature and low PO2 region. The obtained Y123 powder crystals showed superconducting critical temperature (Tc) more than 90 K after oxygenation annealing regardless of formation temperature and PO2. On the other hand, Eu123 and Eu124 phase were co-obtained at low temperature region in air growth and no Eu124 but Eu123 phase was formed at PO2=10-3 atm at temperatures from 500ºC to 700ºC. Therefore, phase relation of Eu123 and Eu124 was slightly different form that of the Y-based system. Tc of Eu123 phase depended on growth temperature and PO2. Tc decreased as growth temperature decreased and PO2 increased. The Tc degradation of Eu123 phase and the phase relations of Eu-system slightly different from Y-system are possibly occurred by the partial substitution of Eu for Ba site in E123 crystal structure by KOH flux. RE123 films on single crystalline substrates were obtained from KOH flux. This indicates that KOH flux method has a process potential for the application to the preparation of RE123/substrate composite devices. The authors thank F. Nakayama for experimentation discussion. |
Thickness dependent properties of YBCO films grown on CLO/GZO-buffered NiW substrates MALMIVIRTA Mika1, HUHTINEN Hannu1, ZHAO Yue2, GRIVEL Jean-Claude2, PATURI Petriina1 1University of Turku, Finland, 2Technical University of Denmark, Denmark show / hide abstract The growth of YBa2Cu3O6+x (YBCO) films deposited by pulsed laser deposition on a high-quality biaxially textured NiW substrates with chemical-solution-deposited buffer layers, Gd2Zr2O7 barrier and Ce0.9La0.1O2 cap, is systematically investigated. The optimization process is executed by varying the number of laser pulses i.e. the thickness of the film, to get better understanding about the quality of YBCO films near the interface of the buffer layer. The structural characterizations as well as the magnetic and resistivity properties are determined by x-ray diffractometry, atomic force microscopy, and with conventional magnetometry and transport measurements. The structural analysis shows that the YBCO films are fully textured, c-axis out-of-plane, but in-plane 45º oriented grains occur in all the thicknesses. In addition, the full width at half maximum of the YBCO (005) peak increases in 2theta and the c-axis lengthens with increasing film thickness, indicating modified unit cell structure in thicker films. When comparing the superconducting properties with the properties of YBCO films grown on single crystal SrTiO3 substrates, the critical temperature in films on buffered NiW is slightly lower but the transitions are clearly broader. However, remarkable thickness dependent variation in Tc or in Delta Tc cannot be observed. In any case, the obtained results are in the significant role when developing the optimal buffer layer structure for NiW metal substrate based future generation technology solutions. Jenny and Antti Wihuri Foundation and Finnish Cultural Foundation are acknowledged for financial support. |
Microstructure and Superconducting Properties of the YBa2Cu3O7-X Films with the co-doping of BaTiO3 and Y2O3 nanoparticles GU Hongwei1, DING Fazhu1, WANG Hongyan1, QU Fei1, ZHANG Huiliang2, DONG Zebin2 1Institute of Electrical Engineering, Chinese Academy of Sciences, China, 2University of Chinese Academy of Sciences, China show / hide abstract YBa2Cu3O7-x (YBCO) films with co-doping BaTiO3 (BTO) and Y2O3 nanostructures were prepared by metal organic deposition using trifluoroacetates (TFA-MOD) method. The properties of the BTO/Y2O3 co-doped YBCO films with different excess yttrium have been systematically studied by x-ray diffraction (XRD), Raman spectra and scanning electron microscope (SEM). The optimized content of yttrium excess in the BTO/Y2O3 co-doped YBCO films is 10 mol %, and the critical current density (JC) is as high as ~ 17 MA/cm2 (self-field, 65K) by the measurement of magnetic signal. In addition, the Y2Cu2O5 was formed when the content of yttrium excess rising to 24 mol %, which may be result in the deterioration of the superconducting properties and the microstructure. The unique combination of the different types of nanostructures of BTO and Y2O3 in the doped YBCO films, compared with the pure YBCO films and BTO doped YBCO films, enhance the critical current density (JC) not only at self-magnetic field, but also in applied magnetic field. |
Enhanced Jc of YBa2Cu3O7-x – Ag superconducting thin films synthesized through Low-fluorine MOD method LI Chunyan1, LIU Min1, SUO Hongli1 1Beijing University of Technology, China show / hide abstract We have developed a low-fluorine metal organic decomposition method for the synthesis of YBCO precursor solution using methacrylic acid partially replace conventional trifluoroacetic acid (TFA) which have greatly shortened the fabrication period and reduced the release of hazardous gases. By mixing different amount of silver trifluoroactate with YBCO precursor solution to study the doping effect of silver on YBCO thin films coated on LAO single crystal substrates. XRD patterns show that the intensity of the (00l) peaks increase with silver doping implying a better crystallization induced by Ag-doping. SEM measurement indicate that Ag-doped YBCO film remains higher quality in terms of smoothness and connectivity compared with pure YBCO film. Besides, self-field Jc is apparently improved by Ag doping which achieved 4.2 MA/cm2. |
Planarization Y2O3 buffer substrate for biaxially textuxted IBAD_MgO films KO Rock-Kil1, KIM Gwan-Tae1, KANG Boo-Min1, HA Dong-Woo1 1Korea Electrotechology Research Institute, South Korea show / hide abstract The surface roughness of substrate has a significant effect on the initial texture of IBAD_MgO thin films. Biaxially textured MgO thin film layer was deposited on chemical solution derived planarization Y2O3 buffer substrate by IBAD(Ion Beam Assisted Deposition) method for HTS(High temperature superconductor) coated conductor. Planarization Y2O3 layer was prepared on unpolished Hastelloy metal tape using a continuous reel-to-reel solution multi-nano layer coating process. Unpolished Hastelloy substrate has a typical RMS roughness around 21 nm over 5x5 um2 area. Planarization Y2O3 buffer substrates were prepared with various degrees of RMS roughness values between 0.5 and 15 nm. We studied the influence of the surface roughness of the planarization Y2O3 buffer substrate for IBAD_MgO films. |
1A-M-P-05 Sep 7 - Afternoon (2:00-4:00 PM) Materials - MgB2 I |
Synthesis of MgB2 thin films via solution-based approach STRAKA Weston1, CARNES Trever2, REY Chris2, SCHWARTZ Justin1 1NC State University, United States, 2E2P Solutions, United States show / hide abstract Magnesium diboride thin films show promise for use as electronic devices, in RF cavities, and as high field conductors. The most popular method for producing MgB2 thin films is through hybrid physical chemical vapor deposition. This technique utilizes magnesium pellets and diborane gas to yield high quality, epitaxial thin films that exhibit good high field properties and higher-than-bulk Tc. Other techniques have been studied including chemical vapor deposition, pulsed laser deposition, and sputtering. These techniques involve expensive equipment and make scaling up to industrial quantities difficult. Using solution-based approaches to create MgB2 thin films, scalability is increased substantially while cost is kept low. One such process involves synthesizing a magnesium borohydride solution, depositing this solution on various substrates through spin coating and dip coating, and annealing the film to evolve hydrogen and sinter the film. The other approach is to use a magnesium diboride suspension, coat the sample through an electric field, and anneal the sample to sinter the particles. The electronic and magnetic properties of these thin films are shown and compared to epitaxially grown films. |
The influence of processing conditions on MgB2 superconductor obtained by ex-situ spark plasma sintering technique BADICA Petre1, BURDUSEL Mihail1, POPA Stelian1, ENCULESCU Monica1, PASUK Iuliana1, VASYLKIV Oleg2, BORODIANSKA Hanna2, ALDICA Gheorghe1 1National Institute of Materials Physics, Romania, 2National Institute for Materials Science, Japan show / hide abstract Superconducting bulks of MgB2 were prepared by spark plasma sintering under different processing conditions. Samples have a high density above 93%. A heating rate of 20, 110, 235, 355, and 475 K/min was applied for a heat treatment in vacuum. A high heating rate is leading to a sharp superconducting transition in the M-T measurements, but many flux jumps occurred at 5 K in the M-H loops. The sample heated for 475 K/min contains the lowest amount of MgO and MgB4 impurity phases. The sample processed with the lowest heating rate of 20 K/min, has the lowest critical current density Jc(H) in the 5-20 K range. The sample obtained for a high heating rate shows a microstructure with wavy and not well defined grain boundaries, while the sample processed with a low heating rate is composed of grains and blocks with well defined straight edges. An optimum sample showing the highest value of the product Jc(0) x (mu0)Hirr is determined for a heating rate of 110 K/min. In a different set of experiments we have performed heating during SPS in vacuum, Ar or N2 applying between 700 and 1100°C heating rates of 10, 20 and 100 K/min. A lower heating rate for nitrogen processing results in formation of more MgB9N impurity phase and this is accompanied by the decrease of Jc(H). This work was performed within Partnership program - PN II, funded by MEN-UEFISCDI, project No. 214/2014. Authors thank Dr. V. Mihalache for help with XRD measurements. |
Addition of Sb2O5 into MgB2 obtained by ex-situ spark plasma sintering technique BURDUSEL Mihail1, ALDICA Gheorghe2, POPA Stelian2, BADICA Petre2 1Nat. Inst. Mater. Phys.Politehnica U. Bucharest, Romania, 2National Institute of Materials Physics, Romania show / hide abstract Superconducting disks of MgB2 with addition of Sb2O5 with different stoichiometric compositions ((MgB2) + (Sb2O5)x, x = 0.0025, 0.005, 0.015 were obtained by the ex-situ Spark Plasma Sintering (SPS) technique. All added samples have high density (>95%). The critical temperature Tc shows a small variation within 38-38.8K. This result and XRD data suggest that Sb does not enter the lattice of MgB2. X-ray diffraction investigations indicate that impurity phases are Mg3Sb2, MgO, and MgB4. We found that there is an enhancement of the irreversibility magnetic field for the optimum doped sample with x = 0.005 or 0.01 of the Sb2O5 additive. The complex correlation between starting compositions, phases, microstructure and vortex pinning aspects are discussed. This work was performed within Partnership program - PN II, funded by MEN-UEFISCDI, project No. 214/2014. M.B. acknowledges Sectoral Operational Programme Human Resources Development 2007-2013 of the Romanian Ministry of European Funds through the Financial Agreement POSDRU/159/1.5/S/132395. |
Enhanced superconducting and mechanical properties of disc and ring shape MgB2 fabricated by an excess Mg method for large scale applications GECER Sahure1, ERTEKIN Ercan2, KOSA Janos2, YANMAZ Ekrem3, GENCER Ali2 1Ankara university, Turkey, 2Ankara University, Turkey, 3Karadeniz Technical University, Turkey show / hide abstract In this work, an excess Mg technique for MgB2 superconductor was developed by using nano boron. Appropriate amounts of elemental magnesium powder(Mg) and amorphous nano boron (B) powder were mixed in an agate mortar. The excess Mg technique was described as follow: The amount of Mg and B were calculated according to stoichiometric ratio of Mg: B, the quantity of B was kept as calculated amount. The amount of Mg was determined to be double amount of B quantity without considering the calculated value. Therefore, mixture was transferred into a chromium tube which both ends of the tube were tightly closed using chromium lids in an Ar atmospheres and a heat treatment was applied using preheated muffle furnace at 1000 oC for 15 min to allow the rapid reaction of Mg with B. After first reaction, disc and ring shape of bulk materials were produced in a controlled atmosphere using a homemade hot press furnace and followed a furnace sintering step. The transition temperatures (Tc) determined using an ac susceptometer were found to be around 37K which is a typical value of Tc for ordinary MgB2 superconductor. Consequently, the Mg excess method can be accepted as a novel method with improved superconducting properties. Therefore, this preparation method can be easily used for levitation and SFCL applications. This research has been financially supported by Scientific and Technological Research Council of Turkey, TUBITAK (Grant No. 113F205). |
Working with MgB2 - The formation of hazardous B2H6 during processing of MgB2 powder KAUFFMANN-WEISS Sandra1, HÄßLER Wolfgang2, SCHEITER Juliane2, HOLZAPFEL Bernhard1 1Karlsruhe Institute of Technology (KIT), Germany, 2IFW Dresden, Germany show / hide abstract Since the discovery of superconductivity in MgB2, various preparation methods have been developed for films, filaments, or wires of this material. Physical vapor deposition methods require a well-adjusted atmosphere and the prevention of oxygen contamination. Another possibility is the Mg diffusion method where different Mg and B precursors undergo a reaction. Of all the deposition methods for MgB2 films, hybrid physical-chemical vapor deposition has been the most effective one for epitaxial, yet only thin films. A new method for preparing films is using pre-reacted MgB2 powder by the technique called Aerosol Deposition technique which is known for preparation of ceramic films. Multifilament conductors are prepared with the powder-in-tube technique using in-situ and/or ex-situ reacted MgB2 powders. This shows that most promising preparation methods need MgB2 powder. However, the processing of MgB2 as a material itself is difficult. One important aspect is the formation of the hazardous gas B2H6 during processing of MgB2 powder. MgB2 can react with water from the atmosphere and forms B2H6 or higher borides. This gas is harmful by inhalation and flammable. However, this gas is colorless and the odor threshold is higher than the highest permissible concentration of B2H6 in the air at the workplace (AGW value 0.1 ppm). We will demonstrate how B2H6 is formed. In order to do so, we investigated the influence of temperature and humidity on as-received and milled MgB2 powder in a closed system. The B2H6 content is measured by a commercially available Diboran sensor. Finally, we will make a few recommendations for working with MgB2. Work was funded by Federal Ministry of Education and Research (BMBF) through 03SF0480C |
The Effect of Bi2Sr2Ca1Cu2O8+κ addition on superconducting properties of bulk MgB2 obtained by hot-press method TAYLAN KOPARAN Ezgi1, SAVASKAN Burcu2 1Bulent Ecevit University, Zonguldak, Turkey, 2Karadeniz Technical University, Turkey show / hide abstract We present here a detailed investigation of the effects of Bi2Sr2Ca1Cu2O8+κ (Bi-2212) addition on the magnetic and structural properties of bulk MgB2 obtained by hot-press method. The amount of Bi-2212 was varied between 0 and 10wt% (0wt%, 2wt%, 4wt%, 6wt%, 10 wt%) of the total MgB2. All samples were prepared by using elemental magnesium (Mg) powder, amorphous nano boron (B) powder (supplied from Pavezyum Turkish co.) and Bi-2212 powder (purchased from Merck chemical company) by hot-press method. Following hot press process, manufactured compact pellet samples were wrapped in tantalum foil and put into a chromium tube which both ends of the tube were tightly closed using chromium lids in Ar atmosphere. Finally, closed chromium tube was placed in a preheated muffle furnace at 1000 oC for 15 min in Ar atmosphere. After heating process, the closed chromium tube was taken out of furnace and cooled at room temperature. The magnetic field dependence of the critical current density Jc was calculated from the M-H loops. Magnetic field dependence of the pinning force density fp(b) and also Tc was investigated for the different addition level of Bi-2212. The details analysis of the nature of pinning in MgB2 for the different addition level of Bi-2212 has greater importance in order to enhance the Jc in magnetic field. The research gave enlightening information the nature of pinning centers related with critical current density in the magnetic field. Both the authors would like to thank Prof. Dr. Ekrem Yanmaz (at Karadeniz Technical University, Trabzon, Turkey) for his support and encouragement. This work was supported by the Scientific Research Coordination Unit of Bulent Ecevit University of Turkey, with project No. 2013-76962555-03. |
Microstructure and magnetic properties of bulk MgB2 samples WIEDERHOLD Alex1, KOBLISCHKA Michael1, INOUE Kazuo2, MURALIDHAR Miryala2, MURAKAMI Masato2, BERGER Kévin3, DOUINE Bruno3, HAUET Thomas3, NOUDEM Jacques4, HARTMANN Uwe1 1Saarland University, Germany, 2Shibaura Institute of Technology, Japan, 3Université de Lorraine, France, 4CRISMAT-CNRS, France show / hide abstract Disk-shaped, bulk MgB2 superconductors (sample diameter up to 4 cm) were prepared in order to improve their performance for use as superconducting super-magnets. Several samples were fabricated using two different processes, one set using a solid state reaction in pure Ar atmosphere at temperatures ranging from 750 to 950 oC, and another type prepared via high-pressure sintering. On both types of samples, magnetization and transport measurements revealed that at the low reaction temperatures flux pinning at grain boundaries is dominant, which is decreasing on increasing temperature. At the highest reaction temperature, jc was found to increase again indicating a change of the pinning mechanism [1]. In order to clarify this behavior, the samples were characterized in detail by means of transmission electron microscopy (TEM) and transmission electron backscatter diffraction (t-EBSD). [1] M.R.Koblischka et al., IEEE Trans. Magn. 50, 9000504 (2014). |
Electron paramagnetic resonance spectroscopy studies on the defect structure of MgB2 superconductor BATENI Ali1, ERDEM Emre2, REPP Sergej2, STEFAN Weber2, ACAR Selcuk3, KOKAL Ilkin3, HÄßLER Wolfgang4, SOMER Mehmet1 1Koc University, Turkey, 2University of Freiburg, Germany, 3Pavezyum Kimya Sanayi, Turkey, 4Institute for Solid State and Materials Research Dresden, Germany show / hide abstract Although the various compound morphologies play a decisive role to control its properties, the synthesis method and doping define additional, crucial parameters that markedly impact the nature and concentration of intrinsic or extrinsic defects and the materials’ electronic properties. To this end, it has been reported that carbon doping significantly improves the electromagnetic properties and the critical current density of magnesium diboride (MgB2). Nonetheless, the effect of carbon doping in MgB2 has also been discussed controversially with respect to its substitution site and solubility limit. Moreover, previous studies on C doping into MgB2 were mainly focused on its effect on superconductivity. From the defect structure point of view, the effect of C doping on the electronic properties is equally important and has to be investigated. In this work, the defect structure of C-doped MgB2, and its impact on the material properties will be investigated by electron paramagnetic resonance (EPR) and Raman spectroscopy. EPR is well suited for this task because it provides a direct method to monitor different paramagnetic states of defects and, thus, complements other experimental techniques, such as X-ray powder diffraction (XRPD) and Raman spectroscopy. In this sense, EPR does not only allow for an identification of paramagnetically active intrinsic and extrinsic defects, but also yields insight into the correlation of such defects to the structural and superconductive properties of MgB2. Here, undoped and C-doped MgB2 samples were synthesized using two sets of mixtures prepared from the precursors, amorphous nanoboron and as-received amorphous carbon-doped nanoboron. Mg vacancies and C-related dangling-bond active centers could be distinguished and sp3-hybridized carbon radicals were detected. A strong reduction in the critical temperature Tc was observed due to defects and crystal distortion. The symmetry effect of the latter is also reflected on the vibrational modes in the Raman spectra. This work is financially supported by the Deutsche Forschungsgemeinschaft (DFG) with the grant number Er662/1-2 and Koc University Graduate Program. Authors associated with Koc University would like to thank Koc University Surface Science and Technology Center (KUYTAM). |
Flux-pinning mechanisms in oxide-containing magnesium diboride thin films SHATERNIK Volodymyr1, PRIKHNA Tatyana2, SHAPOVALOV Andrii2, EISTERER Michael3, SHATERNIK Anton2, KOVYLAEV Valerii4 1G.V.Kurdyumov Institute for Metal Physics of the National Academy of Sciences of Ukraine, Ukraine, 2Institute for Superhard Materials of the NASU, Ukraine, 3Atominstitut, Vienna University of Technology, Austria, 4Institute for Problems in Materials Science, Ukraine show / hide abstract The paper presents the results of flux-pinning mechanism investigations by magnetic measurements in the oxide-containing magnesium diboride thin films (MgB2), which are deposited on the dielectric wafers by a magnetron sputtering. The investigations of crystal structure, phase content, relief of the MgB2 thin films have been done by XR-diffraction, SEM microcopy and Auger spectroscopy. It’s demonstrated that depending on the parameters values of the deposition and annealing processes the thin films with various degree of the structure perfection and various phase content could be fabricated.. The density of superconducting critical currents of these films reaches values up to 1,8·1011 – 8,2 · 1010 А/m2 at 10 К and 8·1010 – 2,8 · 1010А/м2 at 20 К in the fields 0-1 Т ( if an external magnetic field is oriented in parallel for the wafer surface) . The magnetic field dependence of the critical current density, jc(B), was analyzed within the frames of the collective pinning models. The various combinations of the Abrikosov vortices pinning types could be realized in the films ( such as a pinning in the places of fluctuation of superconducting critical temperature (δТс -type) or of fluctuation of the free path length (δl-type) ) , on the appearance of which the synthesis conditions can do influence. The MgB2 films that have the combined type of mechanism of the Abrikosov vortices pinning (mainly, in the disordered MgBxOy boundaries in them) are demonstrated the highest values of the superconducting critical current density. |
XPS/XRD/AFM Characterization of Mg1-xAlxB2 Superconductor SALEM Ahmed1, FAIZ Mohammed1, ZIQ Khalil1 1King Fahd University of Petroleum & Minerals, Saudi Arabia show / hide abstract Samples of Mg1-xAlxB2 with different Al content (x = 0 – 0.27) were prepared by solid state reaction technique. The samples were then characterized by X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). The XRD analysis revealed a major phase closed to MgB2 as well as a minor phase MgO. The average grain size was estimated to be about 40 nm for pure MgB2 and was even smaller for the doped samples. The morphology of the samples was investigated by Atomic Force Microscopy (AFM). The XPS analysis revealed that the surface was covered with oxide layers of MgO and B2O2. The common oxide B2O3 was not detected. The amount of MgO was twice as much as B2O2, confirming the higher reactivity of surface Mg than that of B atoms. B 1s spectral region suggests a surface state at about 187.4 eV as well as a bulk state at about 185.8 eV in MgB2. Al substitution for Mg shifted the surface state to higher binding energy while the bulk state was unaffected. The authors thank King Fahd University of Petroleum and Minerals for its support. |