Perpendicular spin valves with ultra-thin ferromagnetic layers

TL;DR

This paper investigates how ultra-thin ferromagnetic layers in perpendicular spin valves influence spin transport, revealing effects of finite size and coherence length on magnetoresistance and spin transfer torque.

Contribution

It introduces a generalized circuit theory approach to analyze finite size effects and proposes a method to measure the ferromagnetic coherence length.

Findings

Finite size effects alter spin transport properties.

Structural asymmetries impact angular magnetoresistance.

Proposed measurement method for ferromagnetic coherence length.

Abstract

We address two finite size effects in perpendicular transport through magnetic multilayers. When the magnetic layer thickness in spin valves becomes of the order or smaller than the spin-flip diffusion length, structural asymmetries affect the transport properties. A magnetic layer with thickness approaching the magnetic coherence length becomes transparent for spin currents polarized perpendicular to the magnetization. We use the generalized magnetoelectronic circuit theory to investigate both effects on the angular magnetoresistance (aMR) and spin transfer torque. We analyze recent aMR experiments to determine the spin-flip diffusion length in the ferromagnet as well as the interface spin-mixing conductance and propose a method to measure the ferromagnetic coherence length.