Magnetization reversal condition for a nanomagnet within a rotating magnetic field

TL;DR

This paper theoretically investigates the conditions for magnetization reversal in a nanomagnet under a rotating microwave magnetic field, deriving formulas for reversal fields and confirming them with numerical simulations.

Contribution

It introduces a theoretical framework for understanding magnetization reversal under rotating fields, including the effects of microwave-induced torque.

Findings

Reversal field exhibits a jump at a specific frequency.

Derived formulas accurately predict reversal fields in different frequency regimes.

Numerical simulations confirm the theoretical predictions.

Abstract

The reversal condition of magnetization in a nanomagnet under the effect of rotating magnetic field generated by a microwave is theoretically studied based on the Landau-Lifshitz-Gilbert equation. In a rotating frame, the microwave produces a dc magnetic field pointing in the reversed direction, which energetically stabilizes the reversed state. We find that the microwave simultaneously produces a torque preventing the reversal. It is pointed out that this torque leads to a jump in the reversal field with respect to the frequency. We derive the equations determining the reversal fields in both the low- and high-frequency regions from the energy balance equation. The validities of the formulas are confirmed by a comparison with the numerical simulation of the Landau-Lifshitz-Gilbert equation.