Discovery of a Bloch point quadrupole constituting hybrid topological strings

Abstract

Topological magnetic (anti)skrymions are robust string-like objects heralded as potential components in next-generation topological spintronics devices due to their manipulability via low-energy stimuli such as magnetic fields, heat, and electric/thermal current. While these two-dimensional (2D) topological objects are widely studied, intrinsically three-dimensional (3D) electron-spin real-space topology remains less explored despite its prevalence in bulky magnets. Here, we capture the 3D structure of antiskyrmions in a single-crystal, precision-doped (Fe_{0.63}Ni_{0.3}Pd_{0.07})_{3}P lamellae using holographic vector field electron tomography at room temperature and zero field. Our measurements reveal hybrid string-like solitons composed of skyrmions with topological number W = -1 on the lamellae's surfaces and an antiskyrmion (W = +1) connecting them. High resolution images uncover a Bloch point (BP) quadrupole (four magnetic (anti)monopoles) positioned along the rectangular antiskyrmion's four corners (Bloch lines), which enable the observed lengthwise topological transitions. Furthermore, we calculate and compare the energy densities of hybrid strings with ideal (anti)skyrmion strings using micromagnetic simulations, which suggest that this composite (anti)BP structure stabilizes via the subtle interplay between the magnetostatic interaction and anisotropic Dzyaloshinskii-Moriya interaction. The discovery of these hybrid spin textures enables topological tunabilty, a tunable topological Hall effect, and the suppression of skyrmion Hall motion, disrupting existing paradigms within spintronics.

11 pages, 4 main figures, 7 extended data figures, 1 extended data table

References in corpus (7)

• Skyrmion Hall Effect Revealed by Direct Time-Resolved X-Ray Microscopy
• Room-temperature antiskyrmions and sawtooth surface textures in a noncentrosymmetric magnet with $S_4$ symmetry
• Direct visualization of three-dimensional shape of skyrmion strings in a noncentrosymmetric magnet
• Tunable Néel-Bloch magnetic twists in Fe3GeTe2 with van der Waals structure
• Doping control of magnetic anisotropy for stable antiskyrmion formation in schreibersite (Fe,Ni)${}_3$P with $S_4$ symmetry
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• Three-dimensional structure and formation mechanism of biskyrmions in uniaxial ferromagnets

Cited by in corpus (9)

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• When Energy and Information Revolutions Meet 2D Janus
• Quantum and classical magnetic Bloch points
• Skyrmion Sliding Switch in a 90-nm-Wide Nanostructured Chiral Magnet
• Hyperbolic Bloch points in ferrimagnetic exchange spring
• Current-controlled creations, deletions, and topological transformations of a single magnetic antiskyrmion in nanostructured cells
• Three-dimensional topological orbital Hall effect caused by magnetic hopfions
• Regularized Micromagnetic Theory for Bloch Points
• Dynamics of antiskyrmion shrinking