Bistability of vortex core dynamics in a single perpendicularly magnetized nano-disk

TL;DR

This study uses microwave spectroscopy and magnetic resonance force microscopy to investigate vortex core bistability in a single nano-disk, revealing how magnetic field influences core polarity and dynamics.

Contribution

It provides the first detailed spectroscopic analysis of vortex core bistability in nano-disks, combining experimental data with theoretical and simulation models.

Findings

Detection of core polarity via frequency splitting

Bistability persists up to large negative magnetic fields

Frequency difference proportional to magnetic field and disk geometry

Abstract

Microwave spectroscopy of individual vortex-state magnetic nano-disks in a perpendicular bias magnetic field, $H$, is performed using a magnetic resonance force microscope (MRFM). It reveals the splitting induced by $H$ on the gyrotropic frequency of the vortex core rotation related to the existence of the two stable polarities of the core. This splitting enables spectroscopic detection of the core polarity. The bistability extends up to a large negative (antiparallel to the core) value of the bias magnetic field $H_r$, at which the core polarity is reversed. The difference between the frequencies of the two stable rotational modes corresponding to each core polarity is proportional to $H$ and to the ratio of the disk thickness to its radius. Simple analytic theory in combination with micromagnetic simulations give quantitative description of the observed bistable dynamics.