Phase control of thermally excited spin precession in ferromagnetic thin films

The precession phase of spins in magnetic medium is a key parameter for encoding and transferring information in spintronic devices. A remaining challenge is the flexible control of the spin precession phase in magnetic materials responding to thermal excitation. Here, we demonstrate ultrafast phase control of a spin precession induced by laser heating in Ni80Fe20 (Py) thin films with double-pulse excitation. A continuous phase tuning is realized by changing the arrival time of the second pulse, where the coverage of phase variation can reach similar to 2 Pi by increasing the laser fluence of the second pulse. The origin of this phase tuning is determined by the combined effects of the orientation of the magnetization at the arrival of the second pulse as well as the direction shift of the effective magnetic field induced by laser heating of the second pulse. Our findings suggest a different pathway for phase tuning of spin precessions under thermal excitation in ferromagnetic materials, which is of great importance for further spintronic applications.