Vorticity of magnetic vortices controlled by exchange bias and shape anisotropy in polygonal nanomagnets

Abstract The vorticity of the magnetic vortex in a polygonal nanomagnet is controlled by the exchange bias and the shape anisotropy using micromagnetic simulations. The vortex vorticities for the triangular, pentagonal and heptagonal nanomagnets are analyzed by applying saturated magnetization and demagnetization along different in-plane directions with various vortex exchange bias field. The vorticity appears to be CW or CCW in turn at different in-plane directions. The proportion of the CW or CCW vorticity changes according to the bias field. The vorticity is always CW or CCW regardless of the in-plane magnetization direction when the bias field reaches a threshold. The bias field threshold decreases with increasing the side number, from triangular, pentagonal to heptagonal, meaning that the contribution of the shape anisotropy weakens when the nanodisk resembles a circle. Furthermore, the simulations are performed with different nanodisk size. The exchange bias field reaches a maximum when the nanodisk size is 0.5 μm, where the contribution of the shape anisotropy compared to the exchange bias is the largest.