Ultrafast thermo-optical control of spins in a 2D van der Waals semiconductor

Laser pulses provide one of the fastest means of manipulating electron spins in magnetic compounds and pave the way to ultrafast operation within magnetic recording, quantum computation and spintronics. However, effective management of the heat deposited during optical excitation is an open challenge. Layered two-dimensional (2D) van der Waals (vdW) materials possess unique thermal properties due to the highly anisotropic nature of their chemical bonding. Here we show how to control the rate of heat flow, and hence the magnetization dynamics, induced by an ultrafast laser pulse within the 2D ferromagnet Cr₂Ge₂Te₆. Using time-resolved beam-scanning magneto-optical Kerr effect microscopy and microscopic spin modelling calculations, we show that by reducing the thickness of the magnetic layers, an enhancement of the heat dissipation rate into the adjacent substrate leads to a substantial reduction in the timescale for magnetization recovery from several nanoseconds down to a few hundred picoseconds. Finally, we demonstrate how the low thermal conductivity across vdW layers may be used to obtain magnetic domain memory behaviour, even after exposure to intense laser pulses. Our findings reveal the distinctive role of vdW magnets in the ultrafast control of heat conduction, spin dynamics and non-volatile memory.