TIME-DOMAIN INVESTIGATION OF ACOUSTICALLY AND THERMALLY DRIVEN MAGNONS

This thesis is the result of the research program carried out as Ph.D. student of the School in Physics, Astrophysics and Applied Physics at Università degli Studi di Milano, which was performed from October 2021 at the Istituto Officina dei Materiali of Consiglio Nazionale delle Ricerche (CNR-IOM) within the Nanoscale Foundries and Fine Analysis (NFFA) facility. My experimental activity led to the implementation of a novel experimental setup within the NFFA-SPRINT laboratory in the premises of the FERMI@Elettra facility (Elettra-Sincrotrone Trieste), and to the establishment of new methodologies for the study of the dynamical properties of matter. In a first experiment, acoustically driven spin wave resonance in polycrystalline Ni thin films was investigated using the Transient Grating (TG) technique. The focus was on examining how the acoustic waves generated in the substrate influence and drive the magnetization dynamics of the Ni thin films via magnetoelastic coupling. In a second experiment, the TG approach has been exploited to drive coherent magnons at a selected wavevector non-relying on the magnetoelastic coupling but rather on the spatially modulated temperature profile generated by the TG excitation mechanism itself. The approach was successfully tested on ferrimagnetic Co78Gd22 alloy. This measurement campaign was conducted as part of an international collaboration aimed at extending this methodology to the Extreme Ultra Violet range, where magnons with wavelengths as short as a few tens of nm can be selectively triggered. Finally, I studied systematically the laser-driven ferromagnetic resonance in Fe5GeTe2 employing tr-Magneto-Optical Kerr Effect (MOKE), implemented in the same setup, as a function of both the external magnetic field and the temperature. The presented results provide insights into the dynamic magnetic properties of the systems studied and highlight promising opportunities for advancing research on coherent magnetization dynamics in the time domain.