Investigation of the rise time and damping of spin excitations in Ni81Fe19thin films

The rise and damping of spin excitations in three Ni81Fe19 films of thickne ss 50, 500, and 5000 Angstrom have been studied with an optical pump-probe technique in which the sample is pumped with an optically triggered magneti c field pulse. The motion of the magnetization was described by the uniform mode solution of the Landau-Lifshitz-Gilbert equation. The rise time of th e pulsed field within the film was smallest in the 50 Angstrom sample and w as generally greater when the pulsed field was perpendicular to the film pl ane. The damping constant was smallest in the 500 Angstrom sample. The vari ations in the rise time and damping are attributed to the presence of eddy currents and structural disorder in the films. Under certain excitation con ditions a second mode was observed in the 5000 Angstrom sample which we bel ieve to be a magnetostatic surface mode. (C) 2001 American Institute of Phy sics.