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.

Nd doped Y0.8 Ca0.2 Ba2-x Ndx Cu3 Oy YBNCO compounds with x≤.50 have been prepared by the solid state reaction technique. The structure and the superconductivity for YBNCO compounds are characterized. The zero resistance transition temperature T for each sample was measured. T increases with the increase of the content of Nd in YBNCO as xF0. 15, c0 c0 and decreases as xG0.20. X-ray diffraction studies show that there is no structural phase transition in the whole doping range. The dependencies of the lattice constants and some other structural parameters on the content of Nd for the samples YBNCO with xF0.20 have different behaviour than that for the samples with xG0.25. It seems that the uperconductivity of YBNCO is related to the structural changes due to Ca and Nd co-doping. q1999 Published by Elsevier Science B. V. All rights reserved.

Lai. 85Sro. 15Cul-yMy04 ceramic cuprates with M-Zn, Ni, Mg, and). ≤0.30 have been synthesized. The superconduct-ing critical temperatures and the room temperature resistivities for M doping have been determined by a standard four-probemethod. The width of each reflection of X-ray diffraction for each sample is analyzed by Rietveld refinements which is related to the average grain size and the average lattice microstrain. In this way we attempt to explain the stronger suppression for non-magnetic doping such aS Zn or Mg than that for magnetic doping such as Ni.

For GdFe/NiCoO bilayers after field cooling, hysteresis loops at low temperatures are shifted along both the horizontal and vertical axes. The exchange field HE changes from negative values to positive values with increasing cooling field HCF and the coercivity HC acquires a maximum near the crossover of HE.At 5K, HE and HC at HCF=3 T and the peak height DHC are proportional to the inverse GdFe layer thickness. At HCF=3 T, HE is always positive in the temperature region from 5 to 350K. At low HCF, however, HE is negative at low temperatures and becomes positive at high temperatures. These results can be ascribed to antiferromagnetic coupling between GdFe and NiCoO layers.