Control of Magnon Dynamics in Layered Ferromagnet Fe3.6Co1.4GeTe2 by Femtosecond Laser Pulses

Achieving efficient control of magnetism in two-dimensional (2D) ferromagnetic materials promises new functionalities for spintronics and magnonics in atomically thin devices. We demonstrate control of magnon dynamics, using femtosecond laser pulses, in a ferromagnetic van der Waals (vdW) material, Fe3.6Co1.4GeTe2. The magnon amplitude, frequency, and lifetime, are manipulated and monitored by transient magneto-optical Kerr spectroscopy. We show strong and continuous modulation of magnon dynamics as a function of excitation laser pulse polarization. The observations suggest the modification of the effective demagnetization field and magnetic anisotropy by the pump laser pulses can be due to anisotropic optical absorption. This implies that excitation laser pulses are able to modify the local spin environment, which enables the launch of magnons with tunability. Our theoretical calculations confirm the anisotropic optical absorption of different crystal orientations. Our findings suggest a new route for the development of opto-spintronic or -magnonic devices.