We report a range of experiments designed to test the efficacy of spin polarized injection from colossal magnetoresistive material (CMR) into high temperature superconductors (HTS). These include traditional transport measurements, studies of CMR/YBCO contacts, measurements of penetration depth and studies of the effect of spin-injection on the critical state of square thin films and rings. We have used pulsed currents to minimize heating and have made comparisons with the non-magnetic homologue of CMR LaNiO3. Our experiments provide evidence that there is a measurable effect, but that it is small and mainly confined to 10–20 nm of the YBCO surface. Current gain of about 0.2 has been observed.
ABSTRACTWe briefly review our data on MOCVD growth problems of sandwich stacked heterostructures based on Bi-Sr-Ca-Cu-O and YBa2Cu3O7 high temperature superconductors. Non-superconducting layers were (Ca, Sr)CuO2, (Ca, Ba)CuO2 and Bi4Ti3O12. Structures were with c-axis normal or inclined with about 45° vs. the surface of the substrate. Film-substrate lattice relationship, growth mechanism and the resulting morphology controlling roughness and uniformity, stability domain of the phases and inter diffusion are all important aspects toward significant progress in the field. Our analysis indicates that requirements are more severe for non-c-axis heterostructures, and suggest some ideas for further improvements.
AbstractThin films of ZrO2, BaF2, and noble metals on TiN have been examined by RBS as potential diffusion barriers between Si(100) substrates and high-temperature superconductors. As best result so far, a buffer layer of 260 nm ZrO2 enabled the growth of a 230 nm film of YBa2Cu3O7-x, which had been deposited by laser ablation. The relatively low zero resistance temperature of about 60 K may result from some interdiffusion between YBaCuO components and the ZrO2 layer or from holes in the film. A 520 nm BaF2 layer was able to prevent Si outdiffusion towards the surface, when exposed to an oxidizing ambient at typical YBa2Cu3O7-x deposition temperatures between 750 and 800°C. A strong reaction between YBaCuO components and BaF2, however, resulted in non-superconducting films. At high temperatures in oxidizing ambient the noble metal/TiN/Si samples suffered severely from oxidation and surface roughening.
ABSTRACTThe successful methods for laser ablation and deposition of epitaxial thin films of metal oxides, especially the high-temperature superconductors (HTSC), have been adapted to pulsed laser deposition (PLD) of the narrow-band compound semiconductor HgCdTe, and the wide-band semiconductor β-SiC. Useful film quality is readily obtained in both cases: the HgCdTe films on CdTe wafers function in IR photodetection and the 3-SiC is epitaxial on both Si (100) and (111) wafers.
The scale of features that control the physical properties of engineered materials is ever decreasing. We can investigate the structure of these materials using several techniques. The techniques are usually selected based on the feature size of interest. Typical scales are the millimeter or optical scale, the micron or microscopic scale, and the nanometer or atomic scale. As the feature size decreases, the capabilities of the technique must increase.Typical features that require at least microscopic characterization include particles in super alloys, grain misorientations in high temperature superconductors and thin films, inclusions in steels, reaction products in gas chambers.
Physics of Backscattered Electron Diffraction