Comportamento estático e dinâmico de skyrmions em nanofitas magnéticas curvadas via simulação micromagnética

Abstract

The objective of this work is to study the behavior of skyrmions on a magnetic racetrack with a curved surface, verifying the stability, movement, and changes in the skyrmion radius at the interface of the CoPt material. We use micromagnetic simulations, which consider the dynamics of the magnetization of the spins in the lattice, using the Landau-LifshizGilbert equation, with application of the integration method, to define the configuration of the magnetic moments, considering the energies of the interactions that act in the system with the existence of a skyrmion, namely: isotropic exchange, magnetocrystalline anisotropic, dipolar and Dzyaloshinskii-Moriya. We divided the study into two parts: first, we performed a static study, where we verified the conditions of deformation and annihilation, when the skyrmion is on the open cylindrical surface of positive and negative curvature type, respectively, with variable radius of curvature. Unlike the plane surface, the skyrmion can be deformed into an elliptical shape on positive curvature. At negative curvature, we find a critical radius of curvature, below which the skyrmion is annihilated. In the second part, we performed a dynamic study on a racetrack with a geometric defect in the form of a cylindrical surface with positive or negative curvature, interspersed between two plane surfaces. We studied the deformation and annihilation conditions for various values of the radius of curvature, the width of the geometric defect and the spin-polarized current density used to move the skyrmion in the lattice. We conclude that the width of the geometric defect and the radius of curvature interfere in the annihilation and deformation of the skyrmion, we also observed a marked movement in the direction perpendicular to the current application, even with low current density. Furthermore, we analyzed the shape of the skyrmion by measuring its radius in two perpendicular directions and its dynamic behavior when passing through the geometric defect, recording the positions and velocities of the center of the skyrmion. A force, attractive or repulsive, is induced by the curvature. Thus, the skyrmion can be accelerated until its speed reaches values 14 times greater than on the plane surface. We show that these analytical results of the simulations agree with the theoretical results via Thiele’s equation.