Hopfion rings in a cubic chiral magnet.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 37993571.
- Also identified by DOI 10.1038/s41586-023-06658-5 and PMC identifier 10665190.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Magnetic skyrmions and hopfions are topological solitons<sup>1</sup>-well-localized field configurations that have gained considerable attention over the past decade owing to their unique particle-like properties, which make them promising objects for spintronic applications. Skyrmions<sup>2,3</sup> are two-dimensional solitons resembling vortex-like string structures that can penetrate an entire sample. Hopfions<sup>4-9</sup> are three-dimensional solitons confined within a magnetic sample volume and can be considered as closed twisted skyrmion strings that take the shape of a ring in the simplest case. Despite extensive research on magnetic skyrmions, the direct observation of magnetic hopfions is challenging<sup>10</sup> and has only been reported in a synthetic material<sup>11</sup>. Here we present direct observations of hopfions in crystals. In our experiment, we use transmission electron microscopy to observe hopfions forming coupled states with skyrmion strings in B20-type FeGe plates. We provide a protocol for nucleating such hopfion rings, which we verify using Lorentz imaging and electron holography. Our results are highly reproducible and in full agreement with micromagnetic simulations. We provide a unified skyrmion-hopfion homotopy classification and offer insight into the diversity of topological solitons in three-dimensional chiral magnets.