Dynamic Symmetry Breaking in Chiral Magnetic Systems

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 Néel‐type domain walls (DWs) whose energetics and mobility remain at issue. Here, a new effect is characterized 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. The authors 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 Néel‐type DWs and expands the utility of field‐driven DW motion to probe and control chiral DWs.

Key points in the determination of the interfacial Dzyaloshinskii-Moriya interaction from asymmetric bubble domain expansion

“…Furthermore, sometimes the bubbles do not expand fastest exactly in direction of the applied in-plane field, so an integrated view of the DW velocities along all directions around the starting bubble can give more information to obtain a valid DMI measure. It is also noteworthy that internal domain wall dynamics in some cases have been shown to influence the steady state magnetization profile leading to growth directions that deviate significantly from the in-plane field axis [35].…”

Intrinsic chiral field as vector potential of the magnetic current in the zig-zag lattice of magnetic dipoles

“…However, recent experiments in the rare earth garnets 44 suggest that a proximate high-SOC layer is not required, and the magnetic ion in the magnetic film itself provides the critical SOC responsible for DMI, irrespective of the SOC of the interfacing material. Indeed, in perpendicularly-magnetized iron garnets, rare-earth orbital magnetism has given rise to an intrinsic spin-orbit coupling generating interfacial DMI at mirror symmetry-breaking interfaces 45 . Moreover, recent findings showing that the rare-earth ion substitution and strain engineering can significantly alter the DMI 44 , 46 , remain to be understood.…”

Key Points in the Determination of the Interfacial Dzyaloshinskii–Moriya Interaction From Asymmetric Bubble Domain Expansion

“…Furthermore, sometimes the bubbles do not expand fastest exactly in direction of the applied in-plane field, so an integrated view of the DW velocities along all directions around the starting bubble can give more information to obtain a valid DMI measure. It is also noteworthy that internal domain wall dynamics in some cases have been shown to influence the steady state magnetization profile leading to growth directions that deviate significantly from the in-plane field axis [38].…”