Rocket-like dynamics of ferrimagnetic domain walls in graded materials

TL;DR

This paper reveals that in graded ferrimagnetic materials, domain walls exhibit relativistic-like dynamics with variable mass and a limiting speed, driven by spatial variations in exchange, anisotropy, and magnon velocity gradients.

Contribution

It introduces a novel understanding of domain wall acceleration in nonuniform magnets, highlighting relativistic effects and variable mass dynamics.

Findings

Domain walls are pushed towards lower surface tension regions.

The inertial mass of domain walls is modified by material gradients.

A dominant force from magnon velocity gradients limits wall speed.

Abstract

Domain wall motion underpins emerging spintronic technologies, such as high-speed racetrack devices and THz logic, and accelerating walls quickly is a key challenge on the path to faster devices. Recent experimental advances introduced magnetic materials with non-uniform composition, allowing angular momentum compensation points and fast domain wall motion, although acceleration of domain walls in these materials remains poorly understood. Here, we show that spatial variation of exchange and anisotropy not only pushes the wall towards lower wall surface tension region, but also modifies its inertial mass, giving rise to a variable-mass relativistic dynamics. We find another force, originating from the magnon velocity gradient, that dominates as the wall velocity approaches the magnon speed. Our results identify domain walls in nonuniform magnets as a playground for relativistic physics with variable mass and limiting speed.https://info.arxiv.org/help/prep#comments