Oscillatory Exchange Coupling and Positive Magnetoresistance in Epitaxial Oxide Heterostructures

Oscillations in the exchange coupling between ferromagnetic $La_{2/3}Ba_{1/3}MnO_3$ layers with paramagnetic $LaNiO_3$ spacer layer thickness has been observed in epitaxial heterostructures of the two oxides. This behavior is explained within the RKKY model employing an {\it ab initio} calculated band structure of $LaNiO_3$, taking into account strong electron scattering in the spacer. Antiferromagnetically coupled superlattices exhibit a positive current-in-plane magnetoresistance.Comment: 4 pages (RevTeX), 5 figures (EPS

Oxygen-enrichment of YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7-&#948;</SUB> using the fluidization technique

The oxygen-deficient phase of the high Tc superconductor, YBa2Cu3O7, was oxygen-enriched using the fluidization technique to give good superconducting properties. The normal method of oxygen treatment at 900&#176;C for 24 h and at 600&#176;C for 24 h has been reduced to just one treatment at 600&#176;C for 12 h by the fluidization technique to achieve almost the same strength of superconducting signal for the YBa2Cu3O7 powder, which establishes the attractiveness of the latter route for the large-scale preparation of superconducting material. The particle sizes were in the range 0-90, 90-180 and 180-420 &#956;m. The fluidized particles were crystalline with orthorhombic distortion. Tconset, estimated using the a.c. magnetic susceptibility method, was 91&#183;3 K. The volume fraction of superconducting material in the product was 83&#183;7-85&#183;3%, one of the highest values reported so far for YBa2Cu3O7