Critical current of spin transfer torque-driven magnetization dynamics in magnetic multilayers

TL;DR

This paper investigates the critical current needed for spin transfer torque-driven magnetization dynamics in magnetic multilayers, highlighting the roles of spin pumping and transverse spin current penetration depth, and reproducing recent experimental findings.

Contribution

It introduces a comprehensive model accounting for spin pumping and finite spin current penetration depth, explaining the finite critical current in zero-thickness free layers.

Findings

Critical current remains finite as free layer thickness approaches zero.

Spin pumping primarily determines the residual critical current.

The model successfully reproduces recent experimental results.

Abstract

The critical current of the spin transfer torque-driven magnetization dynamics was studied by taking into account both spin pumping and the finite penetration depth of the transverse spin current. We successfully reproduced the recent experimental results obtained by Chen et al. [Phys. Rev. B {\bf 74}, 144408 (2006)] and found that the critical current remains finite even in the zero-thickness limit of the free layer. We showed that the remaining value of the critical current is determined mainly by spin pumping.