Dynamic Symmetry Breaking in Chiral Magnetic Systems

• Published in: Advanced materials (Weinheim) Vol. 33; no. 39; pp. e2101524 - n/a
• Main Authors: Brock, Jeffrey A., Kitcher, Michael D., Vallobra, Pierre, Medapalli, Rajasekhar, Li, Maxwell P., De Graef, Marc, Riley, Grant A., Nembach, Hans T., Mangin, Stéphane, Sokalski, Vincent, Fullerton, Eric E.
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.10.2021; Wiley Blackwell (John Wiley & Sons)
• Subjects: Asymmetry; Broken symmetry; chiral domain walls; Chirality; Domain walls; Dzyaloshinskii–Moriya interactions; Ferromagnetism; Field strength; magnetic thin films; Materials science; Symmetry
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.202101524

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. Novel domain growth behaviors are observed with respect to in‐plane magnetic fields in [Co/Ni/Pt] multilayers with chiral Néel‐type domain walls (DWs), including growth perpendicular to the in‐plane field axis. Accounting for steady‐state DW dynamics, the reported model successfully predicts the magnetization and energetic profiles that promote these asymmetries. These results expand the utility of DW motion in probing chiral magnetism.