Current driven spin-orbit torque oscillator: ferromagnetic and antiferromagnetic coupling

TL;DR

This paper theoretically investigates how Rashba spin-orbit coupling influences spin torque oscillators in synthetic ferromagnetic and antiferromagnetic structures, revealing conditions for stable oscillations and phase diagram modifications.

Contribution

It provides an analytical and numerical analysis of the impact of Rashba spin-orbit coupling on STO stability and phase diagrams in synthetic magnetic multilayers.

Findings

Rashba coupling induces anti-damping near collinear states.

It significantly enlarges the STO phase diagram.

STO phases can persist deep into the antiferromagnetic regime.

Abstract

We consider theoretically the impact of Rashba spin-orbit coupling on spin torque oscillators (STOs) in synthetic ferromagnets and antiferromagnets that have either a bulk multilayer or a thin film structure. The synthetic magnets consist of a fixed polarizing layer and two free magnetic layers that interact through the Ruderman-Kittel-Kasuya-Yosida interaction. We determine analytically which collinear states along the easy axis that are stable, and establish numerically the phase diagram for when the system is in the STO mode and when collinear configurations are stable, respectively. It is found that the Rashba spin-orbit coupling can induce anti-damping in the vicinity of the collinear states, which assists the spin transfer torque in generating self-sustained oscillations, and that it can substantially increase the STO part of the phase diagram. Moreover, we find that the STO phase can extend deep into the antiferromagnetic regime in the presence of spin-orbit torques.