Magnetization Dynamics Symmetry in Spin Torque Induced Magnetization Switching

Xiaobin Wang

doi:10.3390/sym2020999

Abstract

Magnetization dynamics symmetry plays important roles in magnetization switching. Here we study magnetic field and spin torque induced magnetization switching. Spin moment transferring from polarized itinerant electrons to local magnetization provides a magnetization switching mechanism without using external magnetic field. Besides its importance in fundamental magnetization switching dynamics, spin torque magnetization switching has great application potential for future nanoscale magnetoelectronic devices. The paper explores magnetization dynamics symmetry effects on spin torque induced magnetization switching, and its interactions with random fluctuations. We will illustrate the consequences of magnetization dynamics symmetry on the critical switching current magnitude and the thermal stability energy of spin torque induced magnetization switching, which are the two most important design criteria for nanoscale spin torque magnetic devices. The concept of Logarithmic magnetization susceptibility is used to extract symmetry and damping information on spin torque induced nonlinear magnetization dynamic processes, and provides paths to control spin torque induced switching in a fluctuating environment.

Highlights

Magnetization switching is a fundamental physics problem that has important practical implications
Readability means the magnetization equilibrium state is stable under disturbances, such as random thermal fluctuation, disturbing magnetic field and polarized current excitations
Hidden in these complex magnetization dynamics are switching behaviors that are of interest to a scientist working on magnetism and an engineer working on device design

Summary

Introduction

Magnetization switching is a fundamental physics problem that has important practical implications. The polarized current electrons, with a net spin moment in the same direction as the reference layer magnetization, will switch the free layer magnetization to the same direction as the reference layer magnetization. At the level of macroscopic magnetization dynamics, spin torque can be approximated through an adiabatic term proportional to m m p and non-adiabatic term proportional to m p where p is a unit vector pointing to the spin polarization direction. For the case of magnetic field lying in the plane X–Z, the energy of the magnetic system is: N (3)

Symmetry Effects on Magnetic Field Induced Magnetization Switching

Symmetry Effects on Critical Current of Spin Torque Induced Magnetization

Symmetry Effects on Magnetic Element Stability under Spin Torque Excitation

E H c M sV 1

N z N y N x 2 N z N y N x

Conclusions