Theoretical Prediction of a Rotating Magnon Wave Packet in Ferromagnets

TLDR

Magnons exhibit cyclotron‑like motion without charge, unlike electrons whose rotation is driven by the Lorentz force. The study theoretically demonstrates that a magnon wave packet undergoes both self‑rotation and edge‑current motion. These motions stem from Berry‑phase effects in momentum space, including Berry curvature contributions in the classical limit of long‑wavelength magnetostatic spin waves with macroscopic coherence length. The rotational dynamics introduce an additional correction term to the magnon Hall effect.

Abstract

We theoretically show that the magnon wave packet has a rotational motion in two ways: a self-rotation and a motion along the boundary of the sample (edge current). They are similar to the cyclotron motion of electrons, but unlike electrons the magnons have no charge and the rotation is not due to the Lorentz force. These rotational motions are caused by the Berry phase in momentum space from the magnon band structure. Furthermore, the rotational motion of the magnon gives an additional correction term to the magnon Hall effect. We also discuss the Berry curvature effect in the classical limit of long-wavelength magnetostatic spin waves having macroscopic coherence length.