Method of analysis of the spectra obtained by microfocused Brillouin light scattering

TL;DR

This paper presents a new modeling approach to interpret microfocused Brillouin light scattering spectra, enabling disentangling mixed microwave excitations in magnetic samples.

Contribution

A simple, direct model for analyzing microfocused BLS spectra that accounts for optical properties, dispersion relations, and sample profiles.

Findings

Model accurately fits experimental spectra from CoFeB films.

The approach clarifies the influence of sample properties on spectral features.

Enables better understanding of spin wave excitations in magnetic materials.

Abstract

Brillouin Light Scattering is a powerful technique to measure the microwave excitations present in a magnetic system. In microfocused mode, the light is focused on the sample using a microscope objective. This accelerates substantially the measurement but results in mixing the response of all microwave excitations into a single spectrum, such that modeling is required to disentangle the contribution of each spin wave. By assuming that a spectrum collected in microfocused mode can be approximated by the sum of all back-scattering spectra that can be collected by the microscope objective, we develop a simple and direct way of interpreting spectra. The model is compared to experimental data collected on a 50 nm thick CoFeB magnetic film. The model allows the understanding of the influence of the optical properties of a sample, of the dispersion relation of the spin wave eigenexcitations and of their thickness profiles, as well as of their populations onto the magnitudes and the lineshapes of the characteristic features of a spectrum