Theory of giant magnetoresistance effects in Fe/Cr multilayers: Spin-dependent scattering from impurities

Abstract

Recent experiments have tested the assumption that a spin-dependent asymmetry in scattering is responsible for the giant magnetoresistance (GMR) in Fe/Cr multilayers by introducing additional impurities (with different spin-dependent scattering asymmetries) at the interfaces. This paper presents a theoretical calculation based on a Boltzmann transport equation approach that is appropriate for these recent experiments. We find that when impurities (Mn,V) are introduced that have a spin-dependent scattering asymmetry similar to that of Cr in Fe, the GMR is not substantially changed. When impurities (Al,Ir) with a spin-dependent scattering asymmetry opposite to that of Cr in Fe are introduced, there is a rapid degradation of the GMR. Our results are compared with experiment, and good agreement is found, provided that the magnitude of the scattering asymmetry in Al is reduced somewhat from low-temperature published values. It is argued that thermal effects could indeed provide such a reduction.