The discovery of colossal magnetoresistance (CMR) 1 in thin film perovskite-like manganites has renewed interest in their possible use in device applications. 2 One of the crucial issues in thin film CMR manganites is the role of finite size effects related to structure on the thin film properties. Due to the restricted geometrical dimensionality of a thin film, a change in the layer thickness changes the metal-to-insulator transition temperature Tc. There exist several key areas for which we do not have a fundamental understanding of the physical processes that are occurring. Many of the problems arise from a poor understanding of the magnetism and structure at, or close to the interface region between the layer and the substrate.

The interface structure and magnetoresistance (MR) for the single spin valve (SV) of Co/Cu/Co structure with a NiO layer at the top or under the bottom were investigated. Glancing incident x-ray reflectivity and x-ray diffuse scatter studies show that the interface roughness of NiO on Co is much larger than that of Co on NiO. The large roughness may be one of the main factors of suppressing spin reflectivity. The interface between NiO and Co becomes more flat after annealing. Different temperature dependence of MR was observed for the top and the bottom SV. We attribute the above phenomena to the competition between the roughness and the exchange effects of the NiO/Co interface.

Structural, magnetic, and calorimetric properties are reported for the La12xPrxBa2Cu3O7 solid olution. The structure remains orthorhombic with lattice parameter increases from a50.3872, b 50.3927, and c51.1709nm for PrBa2Cu3O7 to a50.3903, b50.3944, and c51.1801nm for LaBa2Cu3O7. Substitution of Pr for La depresses Tc from 90 to 52K for La0.5Pr0.5Ba2Cu3O7, which was reported to be a nonsuperconductor. The Pr antiferromagnetic ordering temperature TN decreases monotonically from 18K for PrBa2Cu3O7 to 6K for La0.8Pr0.2Ba2Cu3O7. Thus there is a large range of coexistence of superconductivity and antiferromagnetism for 0.2<x<0.5. The superconductivity and anomalous Pr ordering will be discussed with the R12xPrxBa2Cu3O7 systems R5Y, Nd-Lu.

Thin YBa2Cu3O7-d/La0.67Ca0.33MnO3 (YBCO/LCMO) films were grown on SrTiO3 (STO) substrates by magnetron sputtering technique. The microstructures of the bilayers were characterized and a standard four-probe technique was applied to measure the resistivity of the samples. The interdiffusions at the YBCO/LCMO and LCMO/STO interfaces formed two transient layers with the thickness of about 3 and 2nm, respectively. All the bilayers were well textured along the c axis. At low temperature, the superconductivity can only be observed when the thickness of YBCO is more than 25nm. When the ickness of YBCO is less than 8nm, the bilayers show only ferromagnetism. The superconductivity and ferromagnetism perhaps coexist in the bilayer with the YBCO thickness of 12.5nm. These interesting properties are related to the interaction between spin polarized electrons in the manganites and the cooper pairs in the cuprates.

The mercury-based superconductor Hg-1223 with Pb substituted for Hg has a transition temperature (T RD0 c, the zero-resistance temperature, 135K; T diac, the diamagnetic onset temperature, D 143K) higher than that for pure Hg-1223 compound. The structure of this Pb-doped sample has been nvestigated via neutron powder diffraction. Some selected bond distances are compared to those of Pb-free Hg-1223 cuprate. The contents of Pb and oxygen have been refined. The estimated valence of copper is about 2. 30, which is consistent with that for YBCO superconductor.