Topological charge-dependent motion of the emergent magnetic monopole in soft magnetic elements*

The emergent magnetic monopole, called Bloch point, is a zero-dimensional spin texture where the local magnetization vanishes, characterized by the topological charge q = ±1 in a three-dimensional magnet [1-3]. In contrast to 2D topological spin textures such as skyrmion, monopoles show novel physical behaviors. For example, it shows pinning and depinning behavior at the atomic lattice [4] and ultrafast dynamics in cylindrical nanowires [5]. Despite of intriguing physical behaviors of the monopole, the topological charge-dependent behaviors of the monopole have not been addressed yet due to the difficulty of securing the topologically different monopoles in magnetic materials. Here, we will show the topological charge-dependent motion of the monopole in Ni₈₀Fe₂₀ (Permalloy) elements, observed by utilizing magnetic transmission soft x-ray microscopy [6]. By performing complementary micromagnetic simulation, we found that the transverse deflection of the monopole is associated with the pinning and depinning behavior of the monopole at the atomic lattice. We believe that this work simulates further research on the experimental studies of monopoles.

References

[1] E. Feldtkeller. Z. Angew. Phys. 19, 530–536 (1965).

[2] C. Donnelly et al., Nature 547, 328-321 (2017).

[3] M.-Y Im, H.-S. Han et al., Nature Commun. 10, 593 (2019).

[4] S.-K. Kim, and O. Tchernyshyov. Phys. Rev. B. 88, 174402 (2013).

[5] M. Charilaou et al., Phys. Rev. Lett. 121, 097202 (2013).

[6] H.-S. Han et al., in preparation.