Precessional switching of thin nanomagnets: analytical study

TL;DR

This paper provides an analytical study of precessional magnetization switching in thin nanomagnets, deriving exact trajectories and analyzing the effects of damping and applied fields for potential memory applications.

Contribution

It introduces exact analytical trajectories for magnetization switching and explores the influence of damping and field strength on switching behavior.

Findings

Switching behavior is bounded by a bifurcation at half the anisotropy field.

Switching field increases linearly with damping, with a square root dependence on anisotropy.

Multiple switching trajectories occur at high fields due to energy dissipation.

Abstract

We study analytically the precessional switching of the magnetization of a thin macrospin. We analyze its response when subjected to an external field along its in-plane hard axis. We derive the exact trajectories of the magnetization. The switching versus non switching behavior is delimited by a bifurcation trajectory, for applied fields equal to half of the effective anisotropy field. A magnetization going through this bifurcation trajectory passes exactly along the hard axis and exhibits a vanishing characteristic frequency at that unstable point, which makes the trajectory noise sensitive. Attempting to approach the related minimal cost in applied field makes the magnetization final state unpredictable. We add finite damping in the model as a perturbative, energy dissipation factor. For a large applied field, the system switches several times back and forth. Several trajectories can be gone through before the system has dissipated enough energy to converge to one attracting equilibrium state. For some moderate fields, the system switches only once by a relaxation dominated precessional switching. We show that the associated switching field increases linearly with the damping parameter. The slope scales with the square root of the effective anisotropy. Our simple concluding expressions are useful to assess the potential application of precessional switching in magnetic random access memories.