Crossover between fast and slow excitation of magnetization by spin torque

TL;DR

This paper investigates two distinct mechanisms by which spin transfer torque destabilizes magnetization in a ferromagnetic multilayer, revealing a crossover between fast and slow excitation processes depending on magnetic field strength and current direction.

Contribution

It identifies and characterizes a crossover between fast and slow magnetization excitation mechanisms driven by spin transfer torque in multilayer structures.

Findings

Fast transition occurs at low magnetic fields.

Slow transition with oscillations dominates at high fields.

The fast transition is the only mechanism for opposite current direction.

Abstract

A crossover between two mechanisms destabilizing the magnetization in equilibrium by the spin transfer effect is found in a ferromagnetic multilayer consisting of an in-plane magnetized free layer and a perpendicularly magnetized pinned layer, where an in-plane magnetic field is applied, and electric current flows from the pinned to the free layer. A fast transition from the in-plane to the out-of-plane state occurs in the low-field region, whereas a slow transition with small-amplitude oscillation becomes dominant in the high-field region. On the other hand, only the fast transition mechanism appears for the opposite current direction.