Dynamics of coupled vortices in layered magnetic nanodots

TL;DR

This paper investigates the vortex dynamics in layered magnetic nanodots with two ferromagnetic cylinders separated by a non-magnetic spacer, revealing how interlayer magnetostatic interactions influence their eigenmodes and frequencies.

Contribution

It provides analytical predictions and micromagnetic simulations of vortex eigenmodes in layered nanodots, highlighting the impact of geometry and interlayer interactions.

Findings

Two eigenmodes predicted and confirmed: GHz and MHz range.

Eigenfrequencies strongly depend on geometrical parameters.

Magnetostatic effects dominate vortex dynamics.

Abstract

The spin dynamics are calculated for a model system consisting of magnetically soft, layered nanomagnets, in which two ferromagnetic (F) cylindrical dots, each with a magnetic vortex ground state, are separated by a non-magnetic spacer (N). This permits a study of the effects of interlayer magnetostatic interactions on the vortex dynamics. The system was explored by applying the equations of motion for the vortex core positions. The restoring force was calculated taking into account the magnetostatic interactions assuming a realistic surface charge free spin distribution. For tri-layer F/N/F dots with opposite chiralities and the same core polarizations (lowest energy state), two eigenmodes are predicted analytically and confirmed via micromagnetic simulations. One mode is in the sub-GHz range for submicron dot diameters and corresponds to quasi-circular rotation of the cores about the dot center. A second mode is in the MHz range corresponding to a small amplitude rotation of the mean core position. The eigenfrequencies depend strongly on the geometrical parameters of the system, suggesting that magnetostatic effects play a dominant role in determining the vortex dynamics.