Magnetization reversal and nonexponential relaxation via instabilities of internal spin waves in nanomagnets

TL;DR

This paper investigates how internal spin wave instabilities cause magnetization reversal and nonexponential relaxation in nanomagnets, revealing fast initial decay followed by slow tail behavior through analytical and numerical methods.

Contribution

It introduces a detailed analysis of linear and exponential spin-wave instabilities and their role in magnetization dynamics in nanomagnets, including analytical relaxation rates and simulation results.

Findings

Magnetization exhibits rapid initial decay during reversal.

Relaxation follows a nonexponential, slow tail at later stages.

Numerical simulations confirm strong magnetization decrease and recovery.

Abstract

A magnetic particle with atomic spins ordered in an unstable direction is an example of a false vacuum that decays via excitation of internal spin waves. Coupled evolution of the particle's magnetization (or the vacuum state) and spin waves, considered in the time-dependent vacuum frame, leads to a peculiar relaxation that is very fast at the beginning but slows down to a nonexponential long tail at the end. The two main scenarios are linear and exponential spin-wave instabilities. For the former, the longitudinal and transverse relaxation rates have been obtained analytically. Numerical simulations show that the particle's magnetization strongly decreases in the middle of reversal and then recovers.