Ultrafast control of coherent spin precession in ferromagnetic thin films via thermal spin excitation processes induced by two-pulse laser excitation

Abstract

We investigate the laser-induced spin precession dynamics in ferromagnetic $\mathrm{N}{\mathrm{i}}_{0.8}\mathrm{F}{\mathrm{e}}_{0.2}$ thin films by using a time-resolved magneto-optical Kerr effect (TR-MOKE) measurement with two pump pulses. By changing the time interval between the pump pulses, the amplitude of the TR-MOKE signal is strongly modulated according to the phase of the TR-MOKE signal at the time when the second pulse arrives. The change in the oscillation amplitude can be explained with the temporal evolution of the spin precession induced by laser heating, as shown with a numerical simulation. We conclude that the ultrafast control of coherent spin precession dynamics is possible by multiple pump pulses via thermal excitation.