Image:

(a) Time-domain and (b) frequency-domain maps of the time-resolved Faraday signal obtained on SiO2(10nm)/Ni(40nm)/SiO2 for a Transient Grating pitch of Λ = 2.54 μm. The magnetic field is swept from positive to negative values. In panel (b) the horizontal dashed lines highlight the frequency of the TG-pumped Rayleigh Surface Acoustic Wave (RSAW) and Surface Skimming Longitudinal Wave (SSLW).

Abstract:

Acoustically and Thermally driven Magnetization Dynamics

Marta Brioschi^a,b,

^a Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, 20133 Milano, IT
^b IOM – CNR, Area Science Park, 34149 Trieste, IT

Controlling coherent collective spin excitations (magnons) in novel magnetically ordered materials is essential for the development of energy-efficient information technologies. We present how the transient grating (TG) approach can be effectively applied to both magnetoelastic and magnonic studies. In this all-optical pump-probe technique, a pitch-tunable transient temperature profile is created through the interference of two pump pulses (300 fs, 1030 nm), which can initiate both acoustic and magnetic dynamics. Consequently, coherent magnons can be pumped by TG-induced acoustic waves, and with an appropriate external magnetic field, these acoustic waves can also drive spin wave resonances. Moreover, coherent magnons can arise from the relaxation of the TG-induced temperature profile, independently from magnetoelastic coupling. We provide complementary measurements in both the optical and EUV ranges to demonstrate how the TG technique can serve as a powerful tool for investigating coherent magnons over a broad range of wavevectors (from μm⁻¹ to nm⁻¹). Lastly, using a single-pump scheme, we examined magnetization dynamics in an 8-nm-thick van der Waals Fe₅GeTe₂ thin film. Specifically, we studied laser-driven ferromagnetic resonance (FMR) via time-resolved magneto-optical Kerr effect (tr-MOKE) measurements, varying both temperature and external magnetic field. This allowed for a systematic characterization of the FMR frequency and effective Gilbert damping.