Nutation Wave as a Platform for Ultrafast Spin Dynamics in Ferromagnets

TL;DR

This paper introduces the concept of nutation waves in ferromagnets, revealing a new collective excitation that enables ultrafast spin dynamics with potential experimental detection via neutron scattering.

Contribution

It uncovers the nutation wave as a novel collective excitation in ferromagnets, combining analytic and numerical methods, and links it to relativistic particles acquiring mass through a topological gauge field.

Findings

Nutation waves are identified as a new collective excitation in ferromagnetic systems.

Nutation particles, 'nutatons', are relativistic massive particles influenced by a topological gauge field.

The nutation wave spectrum could be observed in inelastic neutron scattering experiments.

Abstract

At short time scales the inertia term becomes relevant for the magnetization dynamics of ferromagnets and leads to nutation for the magnetization vector. For the case of spatially extended magnetic systems, for instance Heisenberg spin chains with isotropic spin-exchange interaction, this leads to the appearance of a novel collective excitation, the "nutation wave", whose properties are elucidated by analytic arguments and numerical studies. The one--particle excitations can be identified as relativistic massive particles. These particles, the "nutatons", acquire their mass via the Brout-Englert-Higgs mechanism, through the interaction of the wave with an emergent topological gauge field. This spin excitation would appear as a peak in the spectrum of the scattering structure factor in inelastic neutron scattering experiments. The high frequency and speed of the nutation wave can open new paths for realizing ultrafast spin dynamics.