Brillouin light scattering spectroscopy of parametrically excited dipole-exchange magnons

TL;DR

This study uses Brillouin light scattering spectroscopy to analyze parametrically excited dipole-exchange magnons in yttrium-iron garnet films, revealing mode excitation and spectrum modifications under different pumping powers.

Contribution

It provides a microscopic Heisenberg model-based interpretation of magnon spectra and elucidates the role of ellipticity and spin stiffness in parametric magnon excitation.

Findings

Lowest volume magnon modes are excited perpendicularly to magnetization.

Magnons exhibit highest ellipticity of precession, indicating lowest parametric generation threshold.

Magnon spectrum softens with increased pumping power.

Abstract

The spectral distribution of parametrically excited dipole-exchange magnons in an in-plane magnetized epitaxial film of yttrium-iron garnet was studied by means of frequency- and wavevector-resolved Brillouin light scattering spectroscopy. The experiment was performed in a parallel pumping geometry where an exciting microwave magnetic field was parallel to the magnetizing field. It was found that for both dipolar and exchange spectral areas parallel pumping excites the lowest volume magnon modes propagating in the film plane perpendicularly to the magnetization direction. In order to interpret the experimental observations, we used a microscopic Heisenberg model that includes exchange as well as dipole-dipole interactions to calculate the magnon spectrum and construct the eigenstates. As proven in our calculations, the observed magnons are characterized by having the highest possible ellipticity of precession which suggests the lowest threshold of parametric generation. Applying different pumping powers we observe modifications in the magnon spectrum that are described theoretically by a softening of the spin stiffness.