Ferromagnetic resonance force spectroscopy of individual sub-micron size samples

TL;DR

This paper demonstrates how ferromagnetic resonance force spectroscopy using MRFM can analyze individual sub-micron ferromagnetic samples, providing detailed spin-wave mode data and validating models with experimental results.

Contribution

It introduces a detailed methodology for applying MRFM to measure FMR spectra of individual sub-micron samples and compares experimental data with analytical and micromagnetic models.

Findings

Quantitative FMR data obtained from MRFM measurements.

Good agreement between experimental results and both 2D analytical and 3D micromagnetic models.

Analysis accounts for symmetry breaking and misalignment effects.

Abstract

We review how a magnetic resonance force microscope (MRFM) can be applied to perform ferromagnetic resonance (FMR) spectroscopy of \emph{individual} sub-micron size samples. We restrict our attention to a thorough study of the spin-wave eigen-modes excited in permalloy (Py) disks patterned out of the same 43.3 nm thin film. The disks have a diameter of either 1.0 or $0.5 \mu$m and are quasi-saturated by a perpendicularly applied magnetic field. It is shown that \emph{quantitative} spectroscopic information can be extracted from the MRFM measurements. In particular, the data are extensively compared with complementary approximate models of the dynamical susceptibility: i) a 2D analytical model, which assumes an homogeneous magnetization dynamics along the thickness and ii) a full 3D micromagnetic simulation, which assumes an homogeneous magnetization dynamics below a characteristic length scale $c$ and which approximates the cylindrical sample volume by a discretized representation with regular cubic mesh of lateral size $c=3.9$ nm. In our analysis, the distortions due to a breaking of the axial symmetry are taken into account, both models incorporating the possibility of a small misalignment between the applied field and the normal of the disks.