Skyrmions and emergent electromagnetic responses in frustrated itinerant magnets

Magnetic skyrmion can be formed in centrosymmetric frustrated lattice as well as in noncentrosymmetric lattice with Dzyalloshinskii-Moriya interaction. In particular, RKKY and related higher-order interactions in itinerant magnets with high crystal symmetries tend to stabilize the small-sized skyrmion lattice as well as competing helical-spin magnetic orders. Because of large emergent magnetic field via the high-density skyrmion lattice, gigantic topological Hall effect [1] and Nernst effect [2] are observed, e.g. for hexagonal Gd₂PdSi₃ with triangular-lattice net of magnetic Gd ions, indicating the importance of k-space picture of Berry curvature beyond the conventional real-space picture for the conventional large-sized skyrmion lattice systems. Among them, the breathing Kagome lattice of Gd moments in Gd₃Ru₄Al₁₂ shows the skyrmion phase as well as the similarly short-pitch helical (spin screw) and transverse conical states [3]. The dynamics of these spin-spiral sates under the ac electric-current excitation can lead to the emergent electric field effect on the conduction electron, which in turn generates the emergent electromagnetic inductance (EEMI)[4]. Intriguing features and potentials of the EEMI are discussed in the light of the enhanced emergent electromagnetic responses in chiral magnets.

[1] T.Kurumaji et al., Science 365, 914 (2019).
[2] M. Hirschberger et al., Phys. Rev. Lett. 125, 076602 (2020).
[3] M. Hirschberger et al., Nat. Commun. 10, 5381 (2019).
[4] T. Yokouchi et al., Nature,586, 232 (2020).