Distortion of the Stoner-Wohlfarth astroid by a spin-polarized current

TL;DR

This paper investigates how spin-polarized currents distort the Stoner-Wohlfarth astroid in nano-magnets, revealing a threshold current effect and extending the classical model to include spin-transfer torques.

Contribution

It introduces an extended Stoner-Wohlfarth model that incorporates spin-transfer torques, explaining the observed astroid distortion and threshold current phenomena.

Findings

Spin-transfer most effectively modifies the astroid along the easy-axis.

A threshold current exists below which spin-transfer has no effect.

The extended model accounts for the dip in the astroid caused by spin-transfer.

Abstract

The Stoner-Wohlfarth astroid is a fundamental object in magnetism. It separates regions of the magnetic field space with two stable magnetization equilibria from those with only one stable equilibrium and it characterizes the magnetization reversal of nano-magnets induced by applied magnetic fields. On the other hand, it was recently demonstrated that transfer of spin angular momentum from a spin-polarized current provides an alternative way of switching the magnetization. Here, we examine the astroid of a nano-magnet with uniaxial magnetic anisotropy under the combined influence of applied fields and spin-transfer torques. We find that spin-transfer is most efficient at modifying the astroid when the external field is applied along the easy-axis of magnetization. On departing from this situation, a threshold current appears below which spin-transfer becomes ineffective yielding a current-induced dip in the astroid along the easy-axis direction. An extension of the Stoner-Wohlfarth model is outlined which accounts for this phenomenon.