Statics and Fast Dynamics of Nanomagnets with Vortex Structure

TL;DR

This paper investigates the static and dynamic behaviors of nanomagnets with vortex structures, demonstrating rapid vorticity switching and proposing nano-rings as more stable alternatives for magnetic data manipulation.

Contribution

It introduces a detailed analysis of vortex state switching in nanomagnets, highlighting the potential for ultrafast control and suggesting nano-rings as more stable structures for magnetic storage.

Findings

Vorticity can be switched in 40 ps with strong perpendicular field pulses.

Center polarization switching is limited by damping and is less feasible.

Nano-rings exhibit greater vortex stability compared to circular dots.

Abstract

Within the framework of the Landau-Lifshitz-Gilbert equation, using permalloy parameters, we study the statics and dynamics of flat circular magnetic nano-structures with an in-plane magnetic vortex configuration, putting particular emphasis on the (planar) vorticity of the magnetic state and on the (perpendicular) polarisation of the vortex center (which may be shifted with respect to the center of the circle). These binary degrees of freedom can in principle be used to manipulate two independent bits of information. Studying switching processes induced by in-plane and out-of plane field pulses we find that it is possible to switch the vorticity of the magnetic dot on a time scale of 40 ps in strong enough and short enough perpendicular external field pulses (B_z^ext \approx 0.5 T, duration \approx 40 ps). But for realistically small values of the Gilbert damping, only the vorticity can be switched this fast, and it turns out that it is better to dismiss the center of the circle totally, concentrating on flat 'nano-rings' with an inner radius R_1 and an outer radius R_2. On these 'nano-rings' the vortex state is more stable, and with respect to the switching of the vorticity these structures have similar properties as circular dots.