Low-frequency signature of magnetization nutation in nanomagnets

TL;DR

This paper demonstrates that surface anisotropy in nanomagnets induces detectable nutational motion of magnetization, with analytical and simulation results showing the frequency relationship and potential for experimental observation.

Contribution

It provides an analytical model linking surface anisotropy to magnetization nutation frequencies and validates it with atomistic simulations, revealing a prominent nutation mode.

Findings

Nutation frequency is four times the precession frequency.

Surface anisotropy reduces the precession frequency.

Analytical expressions relate frequencies to nanomagnet parameters.

Abstract

In this work, we show that surface anisotropy in nanomagnets induces a nutational motion of their magnetization at various frequencies, the lowest of which can be described by the macrospin model whose dynamics is governed by an effective energy potential. We derive analytical expressions for the precession and nutation frequencies and amplitudes as functions of the size of the nanomagnet and its atomistic parameters, such as the exchange coupling and the onsite anisotropy. Our analytical model predicts a reduction of the precession frequency with increased surface anisotropy. We also simulate the dynamics of the corresponding atomistic many-spin system and compare the results with the effective model. We thereby show that the first nutation mode induced by the finite size and surface anisotropy occurs at a frequency that is four times larger than the precession frequency, thus lending itself to a relatively easy detection by standard experiments of magnetic resonance.