Ultrafast laser-induced magnetization precession dynamics in FePt/CoFe exchange-coupled films

Femtosecond laser-triggered magnetization precession dynamics in exchange-coupled hard FePt/soft CoFe films has been studied by the time-resolved magneto-optical Kerr effect. The precession frequency is shown to be independent of the CoFe thickness t(CoFe), while linearly proportional to the external field for the sample with t(CoFe) = 7 nm, implying that the magnetization relaxation is governed by a uniform precession mode. The result agrees well with the theoretical prediction based on the Landau-Lifshitz-Gilbert equation. The obtained damping factor alpha similar to 0.13 is quite large and is thought to be dominated by the FePt layer. Additionally, the oscillation amplitude strongly depends on the CoFe thickness with a maximum value occurred at t(CoFe) = 7 nm. (C) 2010 American Institute of Physics. [doi:10.1063/1.3510473]