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We have investigated the influence of Landau quantization both on the field and temperature dependence of some properties of singlet and triplet type4 superconductors. In particular, we consider a multichannel structure of the superconducting gap function, oscillations of the critical temperature with increasing magnetic field and a possible reentrance of superconductivity. In addition, de Haas-van Alphen-like oscillations of the specific heat and its jumps at the critical temperatures have also been analyzed.

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A microscopic model of Ca : YIG minimal system in the form of a pair of the tetrahedral (d) iron -oxygen clusters, separated by the octahedral (a) cluster, coupled in series to the electrodes, is employed in an interpretation of the experimentally observed intriguing behaviour of anisotropic magnetoresistance (MR). Two possible origins of the anisotropy of MR are viewed. The extrinsic one results from orbital contributions to magnetic moments of the central clusters and reveals itself in the external magnetic field. The intrinsic one is caused by different spin polarisation of the left and the right d clusters with respect to the middle a cluster. The effect is connected with a presence of a compensating hole at one of the tetrahedral clusters.

Properties of tunneling conductance spectra of a ferromagnetic-insulator-anisotropic spin triplet superconductor junction are theoretically investigated. The Andreev reflection and transmission of quasiparticles at the interfaces, parallel to the c-axis of the superconductor 2 4 Sr RuO , for unitary p-wave and nonunitary states are discussed. Asymmetry of the Andreev reflection amplitude with respect to the boundary normal is analyzed. Discussion of the resonance peak in this reflection is also performed. The essential influence of the magnitude and direction of the exchange field on the conduction spectrum is investigated.

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Assuming that the holes compensating the Ca + doping charge in Ca +-doped yttrium iron garnet (Ca +: YICx} are located in the p states of oxygen, we study their influence on the superexchange antiferromagnetic d-d coupling, starting with the Anderson periodic Hamiltonian for a system of the narrow-band and wideband electrons, with the p-d hybridization term. Using canonical perturbation theory, we derive explicit expressions for the Kondo-like interaction between a localized iron spin and a p hole, and for the antiferromagnetic superexchange coupling between iron spins. They are based on the second-order and fourth-order p-d hybridizations, respectively. The systematical analysis of the superexchange coupling is performed at T =0 K for both pure and doped YICx. It is shown that the presence of compensating holes can result in a significant decrease in the strength of the superexchange coupling. At a certain concentration of the Ca + ion a change of the sign of the coupling constant is obtained. It turns out that for the charge-transfer model and the Mott-Hubbard insulator model the d-d magnetic coupling is not only different in its value, but also the change of its sign occurs for a different concentration of the doping ions.