P. Przyslupski

Magnetization studies of YBa2Cu3O7−x irradiated by fast neutrons

Abstract Studies of the effect of fast neutron damage on the magnetic hysteresis of YBa 2 Cu 3 O 7−x ceramic samples subjected to fluence of neutrons of 2∗10 16 n/cm 2 up to 6∗10 17 n/cm 2 have been performed. irradiation up to dose of 1∗10 17 did not cause any change in the critical temperature. However it causes a strong increase of the magnetic hysteresis which is presumably connected with the creation of defects. The critical current density at 77 K in H = 10 k0e for the sample irradiated with the dose 1∗10 17 n/cm 2 was estimated to be 520 A/cm 2 as compared to 29 A/cm 2 for the reference non-irradiated sample, non-irradiated sample.

Microwave characterization of Nd0.67Sr0.33MnO3−x thin films for magnetically tunable filters

We report on the microwave properties of Nd0.67Sr0.33MnO3−x (NSMO) and NSMO/YBa2Cu3O7−x thin film heterostructures. The quality factor (Q) and center frequency of a 13 GHz shielded dielectric cavity resonator, with the film comprising one surface, were measured as functions of temperature and direct current magnetic field. The Q versus field data was theoretically simulated using the Landau–Lifschitz–Gilbert dynamic permeability equation thus demonstrating that the microwave losses are determined by the ferromagnetic properties of the films. Our results indicate that the field-dependent permeability μ(B) of NSMO films holds the potential to create magnetically tunable microwave devices.

The influence of fast neutron irradiation on the intra- and intergrain properties of the polycrystalline BiPbSrCaCuO system

Abstract The influence of irradiation by fast neutrons with fluences from 3.3 x 10 16 n / cm 2 up to 3 x 10 18 n / cm 2 on the physical properties of polycrystalline Bi 0.7 Pb 0.3 SrCaCu 1.8 O x was examined. Studies of DC magnetization, AC susceptibility, transport and thermoelectric power were performed. The irradiation caused a decrease of T c , determined from the onset of diamagnetism, by as much as 31 K for a fluence of 3 x 10 18 n / cm 2 . A strong influence of neutron irradiation on both intra- and intergranular properties was observed. The defects within the superconducting grains created by neutrons caused an increase of the pinning forces which enhanced the critical magnetization current. A gradual decoupling of Josephson weak links with increasing neutron fluence was observed in transport and low field magnetization measurements. From the AC susceptibility measurements the irreversibility lines between the flux-creep and flux-flow regions were determined. An increase of the absolute values of thermoelectric power with rising fluence was noticed.

Interplay of superconductivity and ferromagnetism in YBa2Cu3O7/ La1?xSrxMnO3 heterostructures

Oxide manganite/cuprate superlattices are an attractive model system to study the proximity effect in oxide ferromagnet/cuprate superlattices. This report describes recent experimental results obtained on manganite/cuprate heterostructures. The experimental results are discussed in terms of the impact of hole charge transfer from cuprate to manganite layers on the proximity between the oxide ferromagnet and oxide superconductor layers.

CONTROL OF THE VORTEX MOVEMENT AND ARRANGEMENT BY OUT-OF-PLANE MAGNETIC STRUCTURES IN TWINNED YBa2Cu3O7−x/La0.67Sr0.33MnO3 BILAYER

In this article, we consider the magnetic interaction exerted on vortices in a thin YBa2Cu3O7−x film by a La0.67Sr0.33MnO3 layer. The magnetic coupling of the bilayer system was studied and locally imaged by means of magneto-optics. Twin boundaries in the LaAlO3 substrate cause a clear splitting of the manganite magnetic domains with well-defined in-plane magnetization separated by pinned out-of-plane magnetic structures. The vortices nucleated by the external magnetic field interact with the out-of-plane magnetic moments depending on their local structure and magnetic polarization. Different blocking mechanisms (sink or reservoir) are found for the vortex motion perpendicular to twin boundaries, whereas for vortices moving parallel to the out-of-plane magnetic structures either blocking or channelling effect is observed.

Hot isostatic pressing of multifilamentary MgB2 wires in solid state media for large scale application

Multifilamentary MgB2 wires were annealed under the high pressure of low-friction, solid state media such as BN and graphite powders. The idea was to replace the hot isostatic pressing in argon medium, which is beneficial to wires transport properties but is difficult for application on an industrial scale. The experimental results show that annealing in BN or graphite under 200 MPa leads to enhancement of the critical current, similar to that observed earlier for high pressure argon annealing. An unwanted effect of the process is the flattening of the round wires, which after the treatment yields an elliptical cross section with b to a ratio of around 85 ± 5%. Comparison of critical currents and microstructure of samples synthesized with different parameters are presented.

Neutron irradiation damage effect on superconducting and normal state properties of the YBa2Cu3O7 system

Abstract Effect of irradiation by fast neutrons on superconducting and normal state properties of the YBa2Cu3O7 samples is presented. Transport measurements showed a degradation of all superconducting parameters, especially the transport critical current density. Critical current densities obtained from magnetization data exhibited a substantial increase / about 15 times at 77 K and H = 10 kOe/ after the irradiation with the fluence in the range 2.4·1017 ÷ 8.7 · 1017 n/cm2. Such an anomalous bahavior is explained in terms of neutron created defects at intergrain regions and improved intragrain pinning.

Quantitative magneto-optical analysis of twinned YBa2Cu3O7−δ/La1−xSrxMnO3 bilayers

Magneto-optical analysis was performed on YBa2Cu3O7−δ/La1−xSrxMnO3 bilayers grown on twinned LaAlO3 substrates. The twin boundaries in the LaAlO3 substrate induced splitting of the manganite magnetic domains with either in-plane or out-of-plane magnetization, depending on the strontium doping level affecting the magnetic pattern. In the YBa2Cu3O7−δ film, the spontaneous vortex phase, as induced by the out-of-plane magnetic moments in the manganite films, was directly visualized. For vortices nucleated by an external magnetic field, we distinguished different vortex dynamics due to the out-of-plane magnetic moments located either in correlated defects (twin boundaries) or in a homogeneous part of the heterostructure. Vortex guidance over the magnetic domains, dependent only on the relative orientation of the vortex driving force with respect to the local out-of-plane magnetization in the manganite layer, was observed. By means of the inversion of the Biot–Savart law, the local modulations of the supercurrent by the spontaneous vortex phase were imaged. Moreover, a local enhanced/depressed critical current was found across domains of opposite magnetic polarization.

Structure characterization and magnetic properties of oxide multilayers Nd0.67Sr0.33MnO3/YBa2Cu3O7

Abstract Heteroepitaxial growth of multilayer thin films of Nd 0.67 Sr 0.33 MnO 3 /YBa 2 Cu 3 O 7 (NSMO/YBCO) by high-pressure sputtering is reported. We found that critical thickness of YBCO layers for the occurrence of superconductivity in multilayered structure is 3 unit cell. The onset of the temperature of diamagnetic response is lower than the zero resistance superconducting transition temperature. Magnetic hysteresis loops show the coexistence of superconductivity and ferromagnetic order at nm length scale.

Flux pinning by anisotropic arrays of antidots in superconducting thin films

Anisotropic arrays of antidots have been prepared on Y-Ba-Cu-O and Nb thin films by electron-beam lithography. Fast-Fourier-Transform analysis of the magnetization curves for Y-Ba-Cu-O thin film reveals their periodical character which corresponds to the matching effect of the vortex lattice. For niobium thin film, matching peaks can be observed on the decreasing branches of the magnetization curves. Magneto-optical investigations at lower temperatures show unidirectional flux entry and exit along the shorter antidot lattice parameter. In higher magnetic fields, an anisotropic critical state is observed. Our observations strongly suggest formation of anisotropic vortex lattices in the patterned thin films.