Ultrafast optical study of spin wave resonance and relaxation in a CoFe/PtMn/CoFe trilayer film.

We report on our recent study of confined spin wave excitations in a 200 Å CoFe/PtMn/CoFe trilayer film by ultrafast Kerr-rotation experiments. Coherent magnetization precessions were generated and detected by subpicosecond laser pulses. Three precession modes are observed when a magnetic field is oriented in the film plane. The frequencies of two modes increase with the field, while one mode shows no field dependence. The modes are assigned to the exchange-dominated spin wave excitations and the nonhomogeneous dipole mode. We used a comprehensive model of the magnetic eigenmodes and their coupling to light to gain values of the exchange, bulk, and surface anisotropy constants. Further, we investigated spin wave relaxation as a function of the applied field. We calculated an effective damping constant for the uniform precession to be α∼0.012. [ABSTRACT FROM AUTHOR]