Mesoscopic Current-In-Plane Giant Magneto-Resistance

TL;DR

This paper introduces a three-dimensional semiclassical theory extending the Valet-Fert model to describe non-collinear magnetic textures and predicts a mesoscopic CIP-GMR effect in multilayers, with implications for spin torque in nanopillars.

Contribution

It develops a generalized 3D semiclassical model for non-collinear magnetic systems, predicting a new mesoscopic CIP-GMR effect and analyzing complex spin torque behaviors.

Findings

Prediction of non-zero mesoscopic CIP-GMR at the diffusive level.

Identification of non-monotonic spatial variation of GMR.

Significant changes in spin torque with non-uniform magnetization.

Abstract

We develop a three dimensional semiclassical theory which generalizes the Valet-Fert model in order to account for non-collinear systems with magnetic texture, including e.g. domain walls or magnetic vortices. The theory allows for spin transverse to the magnetization to penetrate inside the ferromagnet over a finite length and properly accounts for the Sharvin resistances. For ferromagnetic-normal-ferromagnetic multilayers where the current is injected in the plane of the layers (CIP), we predict the existence of a non zero mesoscopic CIP Giant Magneto-Resistance (GMR) at the diffusive level. This mesoscopic CIP-GMR, which adds to the usual ballistic contributions, has a non monotonic spatial variation and is reminiscent of conductance quantization in the layers. Furthermore, we study the spin transfer torque in spin valve nanopillars. We find that when the magnetization direction is non uniform inside the free layer, the spin torque changes very significantly and simple one-dimensional calculations cease to be reliable.