Skyrmion motion under a spin-Hall current in confined magnetic nanostructures - Presentazione orale by R. Zivieri - Conferenza internazionale

We solve both analytically and numerically Thiele’s equation describing the motion of a magnetic skyrmion in the presence of a spin-Hall current with no external field and by taking into account confinement effects in magnetic nanostructures [1]. In particular, the solution of Thiele’s equation is found for describing the skyrmion motion in a thin magnetic nanostripe. The spin-Hall current injected in the heavy metal combined with the interfacial Dzyaloshinskii–Moriya interaction favors the Néel (hedgehog-like) skyrmion nucleation in the magnetic nanostripe. Confinement effects are modeled by introducing a potential at the boundaries of the magnetic stripe. This potential can be thought of as a repulsive barrier associated to the static magnetization rotation at the stripe borders. The Nèel skyrmion is interpreted as a quasi-particle which interacts repulsively with this barrier. The effect of this interaction is to cause a deviation of the magnetic skyrmion trajectory. When confinement is neglected the Néel magnetic skyrmion moves along an in-plane direction perpendicular to that of the spin-Hall current inside the ferromagnetic nanostripe [2]. Instead, in the presence of confinement effects the trajectory followed by the Nèel skyrmion is perpendicular to that of the spin-Hall current in the central portion of the stripe where the effects of the force arising from the boundary potential are opposites, while it deviates considerably from this direction when the Néel skyrmion approaches the upper (or the lower) border of the stripe placed perpendicularly to the skyrmion velocity. This behavior is interpreted in terms of the scattering of a quasi-particle with the potential barrier created by the rotation of the magnetization on the border. The dependence of this deviation on the stripe magnetic parameters is discussed both analytically and micromagnetically. This work was supported by MIUR-PRIN 2010-11 Project2010ECA8P3 "DyNanoMag". REFERENCES [1] J. Iwasaki, M. Mochizuki, and N. Nagaosa, "Current induced skyrmion dynamics in constricted geometries", Nat. Nanotech. 8, 742 (2013). [2] R. Tomasello, E. Martinez, R. Zivieri, L. Torres, M. Carpentieri, and G. Finocchio, Sci. Rep. 4, 6784 (2014)