Josephson current in superconductor-ferromagnet structures with a nonhomogeneous magnetization

F. S. Bergeret; A. F. Volkov; K. B. Efetov

doi:10.1103/PhysRevB.64.134506

paper

Josephson current in superconductor-ferromagnet structures with a nonhomogeneous magnetization

arXiv:cond-mat/0106510 · doi:10.1103/PhysRevB.64.134506

Abstract

We calculate the dc Josephson current $I_{J}$ for two types of superconductor-ferromagnet (S/F) Josephson junctions. The junction of the first type is a S/F/S junction. On the basis of the Eilenberger equation, the Josephson current is calculated for an arbitrary impurity concentration. If the expression for the Josephson critical current $I_{c}$ is reduced to that which can be obtained from the Usadel equation ( $h$ is the exchange energy, $τ$ is the momentum relaxation time). In the opposite limit $h τ ≫ 1$ the superconducting condensate oscillates with period and penetrates into the F region over distances of the order of the mean free path $l$ . For this kind of junctions we also calculate $I_{J}$ in the case when the F layer presents a nonhomogeneous (spiral) magnetic structure with the period $2 π / Q$ . It is shown that for not too low temperatures, the $π$ -state which occurs in the case of a homogeneous magnetization (Q=0) may disappear even at small values of $Q$ . In this nonhomogeneous case, the superconducting condensate has a nonzero triplet component and can penetrate into the F layer over a long distance of the order of $ξ_{T} =$ . The junction of the second type consists of two S/F bilayers separated by a thin insulating film. It is shown that the critical Josephson current $I_{c}$ depends on the relative orientation of the effective exchange field $h$ of the bilayers. In the case of an antiparallel orientation, $I_{c}$ increases with increasing $h$ . We establish also that in the F film deposited on a superconductor, the Meissner current created by the internal magnetic field may be both diamagnetic or paramagnetic.

13 pages, 11 figures. To be published in Phys. Rev. B

Josephson current in superconductor-ferromagnet structures with a nonhomogeneous magnetization

Abstract

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