Magnetic hopfion rings

Nikolai Kiselev, FZ Juelich

Magnetic solitons are localized magnetization field configurations in crystals that exhibit properties similar to ordinary particles. For example, under different external stimuli such as magnetic fields, temperature gradients, or electric currents, magnetic solitons can move and interact with one another. These characteristics make magnetic solitons promising candidates for applications in information transfer and data storage. The most well-known example of magnetic solitons is skyrmions in chiral magnets. Skyrmions in 2D materials and skyrmion strings in bulk samples represent quasi-two-dimensional configurations. The three-dimensional magnetic solitons, also known as hopfions, were theoretically predicted in several magnetic systems. Hopfions can be conceptualized as closed twisted skyrmion strings. In the simplest scenario, hopfions form toroidal or ring-like structures localized within a small volume of the magnetic sample. We present the first experimental observation of 3D topological magnetic solitons in magnetic crystals, particularly hopfions linked to skyrmion strings in B20-type FeGe, through high-resolution transmission electron microscopy. I will discuss various aspects of hopfion rings, including a highly reproducible protocol for hopfion ring nucleation, the diversity of configurations of hopfion rings linked with one or a few skyrmion strings, hopfion ring zero modes, etc.

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