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Recently, three-dimensional topological spin textures called the magnetic hedgehog lattices (HLs) were discovered in the B20-type compounds MnSi1-xGex [1]. The HLs have periodic arrays of magnetic monopoles and anti-monopoles, which induce interesting transport phenomena, such as the topological Hall effect and the topological thermoelectric transport. However, their stabilization mechanism has not been fully understood thus far. Here we investigate the ground state of an effective spin model with long-range interactions arising from the itinerant nature of electrons by variational calculations and simulated annealing. We find that the HLs are stabilized even at zero field by the synergetic effect of symmetric and antisymmetric interactions from the spin-charge and spin-orbit couplings, respectively. We clarify the full phase diagram in the magnetic field, which includes multiple phase transitions with changes in the number of monopoles and anti-monopoles [2]. We also find that the monopoles and anti-monopoles move, repel, and pair annihilate with topological phase transition by increasing the magnetic field successively [3]. [1] Y. Fujishiro et al., Nat. Commun. 10, 1059 (2019). [2] S. Okumura, S. Hayami, Y. Kato, and Y. Motome, arXiv:1908.05044. [3] S. Okumura, S. Hayami, Y. Kato, and Y. Motome, arXiv:1909.01316.

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Shun Okumura, University of Tokyo
HS III
Contact: Achim Rosch