Slonczewski windmill with dissipation and asymmetry

TL;DR

This paper investigates the stability of the windmill spin-transfer regime in layered magnetic systems, considering dissipation, exchange interaction, and asymmetry, revealing it is generally suppressed except at a specific current.

Contribution

It extends the understanding of windmill spin-transfer dynamics by analyzing the effects of dissipation and asymmetry, identifying conditions for its persistence.

Findings

Windmill rotation is typically destroyed by dissipation and asymmetry.

A unique current value can sustain windmill motion despite these effects.

The study links the phenomenon to current-induced ferromagnetism in isotropic devices.

Abstract

J. Slonczewski invented spin-transfer effect in layered systems in 1996. Among his first predictions was the regime of ``windmill motion'' of a perfectly symmetric spin valve where the magnetizations of the layers rotate in a fixed plane keeping the angle between them constant. Since ``windmill'' was predicted to happen in the case of zero magnetic anisotropy, while in most experimental setups the anisotropy is significant, the phenomenon was not a subject of much research. However, the behavior of the magnetically isotropic device is related to the interesting question of current induced ferromagnetism and is worth more attention. Here we study the windmill regime in the presence of dissipation, exchange interaction, and layer asymmetry. It is shown that the windmill rotation is almost always destroyed by those effects, except for a single special value of electric current, determined by the parameters of the device.