Excitation of Spin Waves in Ferrimagnetic Alloy via Optical Transient Grating Spectroscopy

The investigation of spin waves provides fundamental insights into magnetic materials and is essential for advancing spintronic and magnonic technologies. The Transient Grating (TG) technique, a four-wave mixing method, has been widely used to study collective excitations at controlled wave vectors on the micron to nanometer scale. This study presents an all-optical TG approach for exciting standing dipolar spin waves with a controlled in-plane wave vector in a ferrimagnetic Co78Gd22 thin film, with potential applicability to a broad range of materials. Spin waves with a wavelength of 2.5 μm are excited by the interference of two coherent laser pulses on the sample surface and probed through the diffraction of a third laser pulse. Polarization analysis separates magnetic and thermoelastic signals and enables time-resolved measurements of the spin-wave dynamics.