Boundary conditions for quasiclassical Green functions at superconductor-ferromagnet interface

The quasiclassical equations of superconductivity for a metal with spin-split conduction band are derived. The boundary conditions for the Green functions at the interface between a ferromagnet and a superconductor are obtained. They are valid for the arbitrary magnitude of exchange splitting of a ferromagnet conduction band. © 2000 Elsevier Science B.V. All rights reserved

Boundary resistance in magnetic multilayers

Quasiclassical boundary conditions for electrochemical potentials at the interface between diffusive ferromagnetic and non-magnetic metals are derived for the first time. An expression for the boundary resistance accurately accounts for the law of conservation of momentum as well as essential gradients of the chemical potentials. Conditions are established at which spin asymmetry of the boundary resistance has a positive or negative sign. Dependence of the spin asymmetry and the absolute value of the boundary resistance on the exchange splitting of the conduction band opens up new possibilities for estimating spin polarization of the conduction band of ferromagnetic metals. Consistency of the theory is checked on existing experimental data. © 2006 IOP Publishing Ltd

Oscillations of superconducting transition temperature in strong ferromagnet-superconductor bilayers

The superconducting transition temperature Tc of a "clean ferromagnet-dirty superconductor" bilayer is calculated using boundary conditions derived for the quasiclassical Green's function. This combination corresponds to the majority of experiments, in which Fe, Ni, Co, or Gd are used as a material for the ferromagnetic layer. It is shown that Tc oscillates upon changing thickness of the ferromagnetic layer, in accordance with the experimental observations. © 2003 MAIK "Nauka/Interperiodica"

"Exchange-field-narrowing" process for the inhomogeneously broadened EPR lines in superconductors

A simplified version of the theory, describing the narrowing of inhomogeneously and dipolar broadened EPR lines by the long range exchange in superconductors, is presented. This is the so-called "exchange-field-narrowing" process, in which the localized magnetic moments processing with different frequencies are coupled by the exchange molecular fields, but not by the mutual spin flips. It is also shown that a simple formula for the width of exchange narrowed EPR line can be obtained which takes into account the effects of both the exchange fields and the exchange fluctuations. © 1985

Andreev conductance of a ferromagnet-superconductor point contact

Based on the boundary conditions derived for quasiclassical Green's functions, a theory of Andreev reflection in ferromagnet-superconductor point contacts is constructed. From a comparison with experimental data, the polarization of the conduction band was estimated for a number of ferromagnetic materials used in experiments on Andreev spectroscopy. © 2003 MAIK "Nauka/Interperiodica"

Giant magnetoresistance in quantum magnetic contacts

We present calculations of quantized conductance and magnetoresistance in nanosize point contacts between two ferromagnetic metals. When conductance is open for only one conduction electron spin-projection, the magnitude of magnetoresistance is limited by the rate of conduction electron spin-reversal processes. In the case when both spin-channels contribute to the conductance we analyze the influence of the point contact cross-section asymmetry on the giant megnetoresistance. Recent experiments on magnetoresistance of magnetic point contacts are discussed in the framework of the developed theory. © 2002 Elsevier Science B.V. All rights reserved

Multivalued dependence of the magnetoresistance on the quantized conductance in nanosize magnetic contacts

We calculate the quantized conductance of nanosize point contacts between two ferromagnets for different mutual orientations of the magnetic moments. It is found that the magnetoresistance (MR) is a multivalued function of the quantized conductance at the parallel alignment of the magnetizations σF. This leads us to the conclusion that experimentally observed large fluctuations of MR versus σF are rather due to the conductance quantization than to measurement errors or a poor reproducibility of the results. Using the results of the calculations we are able to understand experimental data obtained by García et al. for MR of the magnetic nanocontacts

Multipole interactions in a LiTmF4 single crystal

We have considered magnetic and magnetoelastic characteristics of a van Vleck paramagnet LiTmF4 taking into account the interaction between thulium ions via the phonon field. We have calculated parameters of the multipole interaction that is caused by the interaction of Tm3+ ions with dynamic lattice deformations of the Bg symmetry. We have presented a self-consistent description of previously published results of measurements of temperature dependences of elastic constants and the nonlinear Zeeman effect in the optical spectrum of the LiTmF4 single crystal, as well as dependences of the magnetostriction on temperature, magnitude, and direction of the external magnetic field. © 2014 Pleiades Publishing, Ltd