Photoinduced magnetic softening of perpendicularly magnetized L10-FePt granular films.

Ultrafast spin dynamics has for the first time been studied in perpendicular magnetized granular films. For FePt continuous films and FePt–MgO and FePt–Ag granular films with femtosecond laser excitations, the coercivity H_C and the saturation Kerr rotation θ_KS are dramatically reduced, accompanied by a sharp increase in the reflectivity R. Afterward, these physical quantities are slowly recovered. The changes in H_C, θ_KS, and R are all different among FePt, FePt–MgO, and FePt–Ag films. The difference is caused by different film thicknesses and in particular by the surface plasmon resonance of metallic nanoparticles. [ABSTRACT FROM AUTHOR]