Brillouin light scattering spectroscopy of magnon-phonon thermal spectra of an in-plane magnetized YIG film in two-dimensional wavevector space

Brillouin Light Scattering (BLS) spectroscopy is widely used for studying collective acoustic and magnetic excitations. In magnetism, it is employed as a versatile tool for measuring the characteristics of magnetic media, visualizing linear and nonlinear spin-wave spatiotemporal dynamics, investigating magnon-phonon interaction effects, and exploring fundamental phenomena such as the Bose-Einstein condensation of magnons. At the same time, magnetic BLS spectroscopy has so far suffered from a lack of possibilities to resolve short-wavelength magnons in arbitrary wavevector directions. Here, we demonstrate two-dimensional thermal magnon and phonon spectra measured in a single-crystal film of Yttrium Iron Garnet (Y3Fe5O12). The wide-range two-dimensional wavevector selectivity is accomplished in the backscattering geometry via independent rotations of the probing beam and the sample plane. The spectra were measured in the range of magnon and phonon wavelengths down to 400 nm and are fully consistent with calculations that take into account exchange, dipole, and elastic interactions. Our results open the way to an in-depth study of the magnon, phonon, and magnon-phonon dynamics of solids.