All-Heat Control of Magnetization Dynamics on Van der Waals Magnets.

Heat dissipation in nanomagnetic devices mediated by femtosecond laser excitation constitutes one of the pressing challenges toward energy-efficient applications yet to be solved. Of particular interest are heterostructures based on 2D van der Waals (vdW) magnets, which benefit from superior interfacial controllability, mechanical flexibility for smart storage platforms, and open-source for large-scale production. However, how heat affects the ultrafast magnetization dynamics in such systems, and/or how the spin dynamics can provide alternative pathways for effective heat dissipation have so far been elusive. Here it is shown that the missing link between magnetization dynamics and heat transport is mediated by the thermal conductivity mismatch between the underneath substrate and the vdW magnet. By modeling the laser-induced ultrafast spin dynamics of three popular vdW materials (CrI, CrGeTe, FeGeTe) of different electronic characteristics across sixteen substrates of distinct chemical composition, it is found that both the demagnetization and remagnetization timescales are very sensitive to the phonon temperature dynamics through the supporting materials, which defines the heating dissipation efficiency at the interface. The process can be further tuned with the thickness of the vdW magnets, where thin (thick) systems result in faster (slower) magnetization dynamics. It is unveiled that the non-thermal nature of spin dynamics in vdW heterostructures creates interfacial spin accumulation that generates spin-polarized currents with dominant frequencies ranging from 0.18 to 1.0 GHz accordingly to the layer thickness and substrate. The findings demonstrate that substrate engineering liaised with the choice of magnetic compounds open venues for efficient spin-heat control, which ultimately determines the optically excited magnetic characteristics of the vdW layers.