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technical paper
Elliptical Ferromagnetic Skyrmions
Magnetic skyrmions are vortex-like spin textures. They are topologically protected from external perturbation and can be driven with extremely low currents. Therefore, they have been paid much attention and they are expected to be applied to the spintronic devices such as the magnetic memories and the logic devices. They can be discovered in so-called chiral magnets which are lacking in the inversion symmetry. The one of the characteristics of the chiral magnets is non-vanishing Dzyaloshinskii-Moriya interaction (DMI). The DMI, which tilts the neighboring spins, is an essential interaction to stabilize the magnetic skyrmions. The characteristics of the DMI are determined by the symmetry of the system. The Neel-type skyrmions are generally observed in Cnv symmetric thin film materials. Recently, the elliptical skyrmions have been observed and they are stabilized in the C2v symmetric systems. This is because the different values of the DMI constants of the x-axis and y-axis can be allowed in the C2v symmetric systems. The elliptical skyrmions have several advantages in comparison with circular skyrmions when applied to the spintronic devices. For example, the skyrmion Hall angles of the elliptical skyrmions can be controlled by changing the shapes of them 1. In this study, we investigate both the dynamics and the phase diagram of elliptical ferromagnetic skyrmions. We consider Co thin films on W as ferromagnetic materials 2. We drive the elliptical skyrmions by applying the spin current in the x-direction. Figures 1 and 2 show the dependences of the velocity (|v|) and the skyrmion Hall angle (θSkHE) on the elliptical ration (b/a), respectively. Here, a (b) is the length of major (minor) axis of the elliptical skyrmions. We find that |v| increases with the decreasing the value of b/a and θSkHE decreases with the decreasing the value of b/a Therefore, the elongated skyrmions along the current direction are useful in comparison with the circular skyrmions when applied to the spintronic devices. At the conference, we are going to show the phase diagrams and discuss the regions where the elliptical skyrmions appear.
References
J. Xia, X. Zhang, M. Ezawa, Q. Shao, X. Liu, and Y. Zhou, Appl. Phys. Lett., Vol. 116, p.022407 (2020)
L. Camosi, J. PeñaGarcia, and J. Vogel et al, New J. Phys., Vol. 23, p.013020 (2021)
Fig. 1 The dependence of |v| on b/a.
Fig. 2 The dependence of θSkHE on b/a.
