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Physik: Magnetische Funktionsmaterialien
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Publication

Editor's suggestion in Physical Review B

Direct imaging of distorted vortex structures and magnetic vortex annihilation processes in ferromagnetic/antiferromagnetic disk structures

Vortex images
(a) Micromagnetic simulations of the magnetic field induced vortex annihilation process mediated by the vortex-antivortex pairs and edge (vortex) state. (b) Sample structure used in the magnetic force microscopy (MFM) imaging experiments. (c) Series of in-field high-resolution MFM scansS for a 4 µm disk structure shows the magnetic vortex annihilation mechanism. The white arrow in (a)(iv) and (c)(iii) indicates the vortex-antivortex state. (d) Close-up of the vortex-antivortex spin-structure indicating two vortex cores (V1 and V2) with opposite polarization and anticlockwise circulation separated by an antivortex (AV). (e) Three-dimensional schematic of a topologically nontrivial vortex-antivortex pair, involving the injection and propagation of a Bloch point through the film. Micromagnetic simulations performed by B. Böhm, disk patterns prepared by L. Ramasubramanian from HZDR, MFM scans performed by S. S. P. K. Arekapudi [1].

Topological objects formed in magnetic thin films, such as skyrmions and vortex structures, and their counterparts (antiskyrmions and antivortex structures), have attracted continued attention over the past 20 years for their distinct magnetic reversal behaviour and potential applications. In particular, the magnetic vortex annihilation process is mediated by the creation and subsequent annihilation of intermediate vortex-antivortex (V-AV) pairs. Creation and annihilation of topologically non-trivial V-AV pairs can involve a magnetic point defect (or singularity) referred to as a Bloch point. Recent work from our groups at TUC and HZDR published in Physical Review B as Editors’ Suggestion [1] closely examines the magnetic vortex annihilation process in simple ferromagnetic disks and exchange coupled ferromagnetic/antiferromagnetic micro-disk structures. In exchange coupled disks, the magnetic vortex structure is shown to be distorted. Further, measurements uncover an unexpected increase in the magnetic field stability of the V-AV state in exchange coupled disk structures [1].

[1] S. S. P. K. Arekapudi et al., Phys. Rev. B 103, 014405 (2021).

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