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Optical absorption and transverse Kerr effect spectra, resistivity, and magnetoresistance of La 1Ϫx Sr x CoO 3 (xϭ0.15,0.25,0.35) films have been studied. The temperature dependences of the optical and magneto-optical properties of the films exhibit features which can be attributed to the transition of the Co 3ϩ ions from the low-spin state (Sϭ0) to the intermediate-spin state (Sϭ1) and to orbital ordering of the Co 3ϩ ions in the latter state. The evolution of the properties influenced by doping with Sr is interpreted on the basis of the phase separation model.

Granular superconductivity effects in polycrystalline samples of RuSr 2 (Gd 1.5 Ce 0.5)Cu 2 O 10−δ , as prepared (by a solid-state reaction method) and annealed (12 h at 845 • C) in pure oxygen at 30 atm, are presented. The resistive transition to the superconducting state of the as-prepared sample is found to be considerably affected by granularity. In particular, an evident kink in the temperature dependence of the resistance R(T) is seen at the temperature, T c0 ≈ 34 K, at which grains become superconducting. The resistive transition depends strongly on the applied current. The family of R(T) curves taken for different transport currents is branched with a branching point at T cJ ≈ 23.2 K. Below this temperature the intergrain Josephson coupling starts to develop. For low current, R decreases with decreasing temperature below T cJ as expected for the transition to the superconducting state, whereas R(T) curves for higher current form a minimum at T ≈ 17.3 K, showing a quasi-reentrant behaviour. The influence of the granular structure of the as-prepared sample shows itself also in the temperature behaviour of the magnetization, M(T), in low field. Application of low magnetic field (below 400 Oe) leads to a broadening of the resistive transitions below T cJ , similar to that caused by increasing the current. Both the current and magnetic field depress the Josephson coupling between the grains, producing a dramatically large effect on the resistive transition. The R(T) and M(T) dependences of the annealed sample show a fairly sharp superconducting transition far less affected by granularity. The results obtained imply that oxygen annealing improves the intergranular connection considerably, but it does not exert much influence on the intragrain superconductivity. No indication of intragrain granularity has

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The analysis of quantum corrections to magnetoconductivity of thin Au films responsible for by the effect of weak electron localization has made it possible to determine the temperature dependences of electron phase relaxation time in the temperature range 0.5--50 K for different degrees of crystal lattice disorder. The disorder was enhanced by irradiating the films in vacuum with 3.5 keV Ar ions. The experimental data clearly demonstrate that the contribution of electron-electron interaction to electron phase relaxation increases with disorder and support the theoretical prediction that the frequency of electron-phonon scattering tends to diminish upon a decrease in electron mean free path. It is found that the spin-orbit scattering rate decreases with disorder. In our opinion, such unusual behavior can take place for thin films at decreasing the electron mean free path provided, that the surface electron scattering contributes significantly to the total spin-orbit scattering.Comment: 15 pages, REVTex, 6 Postscript figures, To be published in Phys. Rev.

Resistivity, thermoelectric power, heat capacity, and magnetization for samples of RuSr2(Gd1.5Ce0.5)Cu2O10−δ were investigated in the temperature range 1.8–300K with a magnetic field up to 8T. The resistive transitions to the superconducting state are found to be determined by the inhomogeneous (granular) structure, characterized by the intragranular, Tc0, and intergranular, Tcg, transition temperatures. Heat capacity, C(T), shows a jump at the superconducting transition temperature Tc0≈37.5K. A Schottky-type anomaly is found in C(T) below 20K. This low-temperature anomaly can be attributed to splitting of the ground term S7∕28 of paramagnetic Gd3+ ions by internal and external magnetic fields.

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