Dynamic symmetry breaking in chiral magnetic systems

TL;DR

This paper uncovers a dynamic symmetry breaking phenomenon in chiral magnetic systems, where domain expansion direction is controlled by magnetic fields, revealing new insights into domain wall dynamics and potential applications in magnetic memory devices.

Contribution

It introduces a novel dynamic symmetry breaking effect in chiral magnetic systems driven by magnetic fields, advancing understanding of domain wall motion beyond static models.

Findings

Domains expand unidirectionally under combined magnetic fields.

Steady-state magnetization profiles are highly asymmetric in elastic energy.

Dynamic symmetry breaking aligns with experimental observations.

Abstract

The Dzyaloshinskii-Moriya interaction (DMI) in magnetic systems stabilizes spin textures with preferred chirality, applicable to next-generation memory and computing architectures. In perpendicularly magnetized heavy-metal/ferromagnet films, the interfacial DMI originating from structural inversion asymmetry and strong spin-orbit coupling favors chiral N\'eel-type domain walls (DWs) whose energetics and mobility remain at issue. Here, we characterize a new effect in which domains expand unidirectionally in response to a combination of out-of-plane and in-plane magnetic fields, with the growth direction controlled by the in-plane field strength. These growth directionalities and symmetries with applied fields cannot be understood from static treatments alone. We theoretically demonstrate that perpendicular field torques stabilize steady-state magnetization profiles highly asymmetric in elastic energy, resulting in a dynamic symmetry breaking consistent with the experimental findings. This phenomenon sheds light on the mechanisms governing the dynamics of N\'eel-type DWs and expands the utility of field-driven DW motion to probe and control chiral DWs.