Laser-induced magnetization dynamics for L1₀-FePt thin films with perpendicular anisotropy

Laser-induced de- and re-magnetization dynamics in perpendicularly magnetized L1₀-FePt films are studied by using a time-resolved magneto-optical pump-probe technique. The observed ultrafast magnetic dynamic behaviors depend on the film thickness and substrate temperature. The thinner FePt film has a relatively larger maximum demagnetization percentage and a slower relaxation rate because of fewer free electrons being in the laser spot area. However, for the same thickness samples, although they have the same maximum demagnetization, their magnetization recovery speed is different. The sample deposited at high T_s exhibits a faster recovery due to the relatively large FePt grains with high magneto-crystalline anisotropy energy. In addition, we find that all the FePt samples reach the maximum demagnetization at an almost same characteristic delay time of 0.9 picoseconds, irrespective of the laser intensity, film thickness, and substrate temperature.