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.

A dynamic model of anisotropic x-ray diffraction is developed using two-wave approximation. A dispersion surface equation is derived for the screw-axis and glide-plane forbidden reflections. Propagation and polarization phenomena of waves are discussed. The deductions show that all these forbidden reflections may be excited except the 00l (l52n11) reflections for a 63 screw axis and the 00l (l56n13) reflections for 61 and 65 screw axes. The general methods are illustrated by their application to the rutile structure. [S0163-1829(99)3330-5]

Cations of Y and Sr co-substituting for La and Ca at A site in La2/3Ca1/3MnO3 compound, a2/3−xYxCa1/3−ySryMnO3, were synthesized successfully by solid-state reaction. X-ray diffraction shows there is only one phase with the dopants of Y and Sr within x≤0.20 or y≤0.19. The lattice parameters along a-, b-, and c-direction remain almost unchanged with x≤0.20. The bond angle of Mn O Mn ncreases from 151.9 for x=0 to 172.7 for x = 0.20 monotonically, which indicates that the Jahn-Teller effect in MnO6 octahedron decreases with increasing x. The temperature dependence of resistance with/without magnetic applied were measured and fitted theoretically. The metal-to-insulator transition emperature, TMI, decreases with increasing the Y content with x≤0.10 while TMI increases slightly with further increasing x. The Y-content dependence of magnetoresistance shows a parabolic behavior. The maximum MR value corresponds to x=0.08-0.10.We attributed these variations in the structure and transportation to the cation disorder due to the cation doping.

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.