We describe a search for the effects of spin-polarized electrons in thin-film bilayers consisting of the high temperature superconductor YBa2Cu3O7-delta and the colossal magnetoresistive material La0.7Ca0.3MnO3 by using penetration depth and critical current measurements. The work differs from that described in other works in that the YBa2Cu3O7-delta is grown with its c-axis lying in the plane of the thin film in order to investigate the effects of proximity suppression and also the injection of a spin-polarized current along the a/b-planes of the YBa2Cu3O7-delta. We see a number of effects including field dependence of the average penetration depth and apparent suppression of the critical current by an injected current, with a gain greater than unity, but we argue that these are explicable in terms of a combination of heating and current summation, without any need to invoke the spin-polarization of the injected current.

Twinning and precipitates in YBa2Cu3O7-delta (YBCO) thin film grown on vicinal SrTiO3 (STO) (100) substrates are investigated. The direction of the in-plane cut of the substrate was chosen to be close to either [010] or [110]. In the former case the surface steps create an anisotropic surface morphology, the YBCO film grows with the c-axis perpendicular to the SrTiO3 (100) crystal lattice plane and the twinning in one in-plane direction can be suppressed. In the latter case the substrate surface is dominated by kinks in the steps, the YBCO film grows with the c-axis perpendicular to the surface geometrical plane and the film is twinned unidirectionally. Films deposited on substrates cut along [110] are rather smooth whereas deep holes are observed in YBCO films grown on substrates vicinally cut along [010]. It is proved by cross-sectional TEM that these holes originate on Y2O3, CuO and Y2O3-CuO precipitates. We find no direct correlation of the precipitate formation with the substrate/film microscopic features, however possible mechanisms are considered.

The complex differential susceptibility of a YBCO film and YBCO–STO–LCMO structures with different thicknesses of the STO layer (0, 2, and 7 nm) is investigated. It is shown that for a YBCO–LCMO structure the temperature of the superconducting transition Tonset and the critical current density jc are observed to decrease in comparison with a pure YBCO film. In a YBCO–STO–LCMO structure, on the contrary, Tonset increases, while jc increases for the structure with the 2 nm thickness of STO and decreases for that with 7 nm of STO. It is conjectured that there is a change of the vortex pinning mechanism as the temperature is lowered.

We report substantial improvement in the critical current in HTS thin film due to the influence of colossal magnetoresistance (CMR) films in YBa2Cu3Ox-based multilayers for spin injection devices. The effect of the CMR strongly depends on the thickness of the HTS, CMR and the intermediate insulator layers. We argue that the improvement in critical current may be due to the self-injection of the spin polarized electrons from the CMR to HTS, opposite to that normally observed in current driven spin injection devices.

We report strong negative magnetoresistance in epitaxial PrBa2Cu3Ox films prepared by laser ablation on SrTiO3 substrates. Magnetoresistance appears at temperatures below ∼50 K. At 10 K its value reaches 90% in a magnetic field of 0.5 T. The magnetoresistance is strongly suppressed near 20 K where the Pr ions undergo antiferromagnetic ordering. Post annealing in flowing oxygen reduces the magnetoresistance by a factor of about three and slightly increases the antiferromagnetic ordering temperature.

The results are presented of experiments on the paramagnetic Meissner effect, the appearance of a net paramagnetic moment when some high-temperature superconductors (especially Bi-Sr-Ca-Cu-O) are cooled in a very small magnetic field. For ease of interpretation the experiments relate exclusively to Bi-Sr-Ca-Cu-O in finely powdered form. Attention is paid not only to the magnetic moment observed during a field cool, but also to the moment remaining during a subsequent zero-held warm and to the moment developed during a field warm following a zero-field cool. The moments observed during a field cool are similar to those reported by ; other authors. A tentative interpretation of the results is made in terms of a model in which there is a concentration within the material of small local moments that can be polarized during a held cool. Information about both the magnitudes of these local moments and their concentrations is deduced. Evidence is presented that the observed local moments are too small to be accounted for by half flux quanta trapped in loops or within grains, such half flux quanta being associated with rr junctions or d-wave pairing. This suggests that either the local moments originate in some other way or the model is incorrect.