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 theta(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, theta(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. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.3007977]