The influence of spin-dependent phases of tunneling electrons on the conductance of a point ferromagnet/isolator/d-wave superconductor contact

The influence of phase shifts of electron waves passing through and reflected by the potential barrier on the Andreev reflection in a ferromagnet/isolator/d-wave superconductor (FIS) contact is studied. It is found that in a superconductor the surface spin-dependent Andreev bound states inside the superconducting gap are formed as a result of the interference of electron-like and hole-like quasiparticles due to repeated Andreev reflections. The peak in the conductance of the FIS contact at the zero potential for the (110)-oriented superconductor disappears rapidly as the polarization of a ferromagnet increases, whereas for the (100)-oriented superconductor it appears. The physical reason for this behavior of conductance is discussed.Comment: 8 pages, 4 figure

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"

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"

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

The influence of spin-dependent phases of tunneling electrons on the conductance of a point ferromagnet/isolator/superconductor contact

The Andreev reflection probability for a ferromagnet/isolator/superconductor (FIS) contact at the arbitrary spin-dependent amplitudes of the electron waves transmitted through and reflected from the potential barrier is found. It is shown that Andreev reflection probabilities of electron and hole excitations in the FIS contact are different. The energy levels of Andreev bound states are found. The ballistic conductance of the point FIS contact is calculated.Comment: e.g.:10 pages, 3 figures added in tex. file: abstract and article's titl

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 momentum conservation law as well as essential gradients of the chemical potentials. Conditions are established at which spin-asymmetry of the boundary resistance has 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 possibility to estimate spin polarization of the conduction band of ferromagnetic metals. Consistency of the theory is checked on existing experimental data.Comment: 8 pages, 3 figures, designed using IOPART styl

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

Ballistic versus diffusive magnetoresistance of a magnetic point contact

The quasiclassical theory of a nanosize point contacts (PC's) between two ferromagnets is developed. The maximum available magnetoresistance values in PC's are calculated for ballistic versus diffusive transport through the area of a contact. In the ballistic regime the magnetoresistance in excess of a few hundred percent is obtained for the iron-group ferromagnets. The necessary conditions for realization of so large a magnetoresistance in PC's, and the experimental results by García et al. are discussed