Probing the anharmonicity of the potential well for magnetic vortex core in nanodot

TL;DR

This study measures the anharmonicity of the potential well confining a magnetic vortex core in a nanodot using MRFM, revealing a positive anharmonic coefficient and significant frequency tunability.

Contribution

It introduces a method to quantitatively measure the anharmonicity of the vortex core potential well in nanodots.

Findings

Anharmonic coefficient is positive and 50% of the parabolic term.

Eigen-frequency varies up to +10% with core displacement.

Method enables calibration of gyrotropic mode tunability.

Abstract

The anharmonicity of the potential well confining the position of the magnetic vortex core is measured dynamically with a Magnetic Resonance Force Microscope (MRFM). The stray field of the MRFM tip is used to displace the core position away from the well minimum. Anharmonicity is then inferred from the relative frequency shift induced on the eigen-frequency of the vortex core translational mode. Traces of these shifts are recorded while scanning the tip above an isolated nanodot, patterned out of a single crystal FeV film. An analytical framework is proposed to analyze the data. It results in a quantitative measurement of the anharmonic coefficient found to be positive and 50% of the parabolic contribution. This calibrates the tunability of the gyrotropic mode by external magnetic fields. In our sample, we observe a variation of the eigen-frequency as high as +10% for a displacement of the vortex core to about one third of the nanodot radius.