Andreev Reflection in Ferromagnet/Superconductor/Ferromagnet Double Junction Systems

TL;DR

This paper develops a theoretical model for Andreev reflection in ferromagnet/superconductor/ferromagnet junctions, explaining how spin-polarized quasiparticles influence magnetoresistance depending on superconductor thickness and other parameters.

Contribution

It introduces a new theory describing Andreev reflection in double junctions, accounting for spin polarization and interface effects, aligning with recent experimental findings.

Findings

Magnetoresistance depends on superconductor thickness and temperature.

Spin-polarized quasiparticles can pass through thin superconductors.

The theory matches recent experimental observations.

Abstract

We present a theory of Andreev reflection in a ferromagnet/superconductor/ferromagnet double junction system. The spin polarized quasiparticles penetrate to the superconductor in the range of penetration depth from the interface by the Andreev reflection. When the thickness of the superconductor is comparable to or smaller than the penetration depth, the spin polarized quasiparticles pass through the superconductor and therefore the electric current depends on the relative orientation of magnetizations of the ferromagnets. The dependences of the magnetoresistance on the thickness of the superconductor, temperature, the exchange field of the ferromagnets and the height of the interfacial barriers are analyzed. Our theory explains recent experimental results well.