Universal Criterion and Phase Diagram for Switching a Magnetic Vortex Core in Soft Magnetic Nanodots

Abstract

The universal criterion for ultrafast vortex-core switching between the up- and down-core bistates in soft magnetic nanodots is investigated by micromagnetic simulations along with vortex-core switching that occurs whenever the velocity of vortex-core motion reaches its critical velocity, ${\upsilon }_{\mathrm{cri}}=(1.66\pm 0.18)\gamma \sqrt{A_{\mathrm{ex}}}$ (e.g., ${\upsilon }_{\mathrm{cri}}=330\pm 37\mathrm{m}/\mathrm{s}$ for Permalloy), with the exchange stiffness $A_{\mathrm{ex}}$ and the gyromagnetic ratio $\gamma$. On the basis of the universality of ${\upsilon }_{\mathrm{cri}}$, phase diagrams for the vortex-core switching event and switching time with respect to both the amplitude and frequency of a circularly rotating magnetic field are calculated.