Symmetry Breaking in the Formation of
Magnetic Vortex States in a Permalloy Nanodisk

Published in “Nature Communications“(Online Publication, July 31, 2012).

Prof. Ono, T., et. al.
(Nanospintronics, Division of Materials Chemistry )

The magnetic vortex in nanopatterned elements is currently attracting enormous interest. A priori, one would assume that the formation of magnetic vortex states should exhibit a perfect symmetry, because the magnetic vortex has four degenerate states. The first direct observation of an asymmetric phenomenon in the formation process of vortex states in a permalloy nanodisk is demonstrated using high-resolution full-field magnetic transmission soft X-ray microscopy. Micromagnetic simulations confirm that the intrinsic Dzyaloshinskii–Moriya interaction, which arises from the spin-orbit coupling due to the lack of inversion symmetry near the disk surface, as well as surface-related extrinsic factors, is decisive for the asymmetric formation of vortex states.

Figure 1. Schematic illustration of magnetic vortex. There are four states depending on the chirality of vortex and the polarity of core ((a)-(d)).

Figure. 2. Experimental images of vortex structures in permalloy nanodisk array. X-ray microscope images of in-plane (a) and out-of-plane (b) magnetic components taken at the remanent state in a 100-nm-thick nanodisks. The sense of rotation of the in-plane magnetization is indicated by a white arrow (a). The black and white spots of the central regions in nanodisks are upward and downward vortex cores, respectively (b). The complete vortex configuration of each nanodisk is also illustrated (c).