Large ultrafast photoinduced magnetic anisotropy in a cobalt-substituted yttrium iron garnet

We demonstrate experimentally that excitation of a Co-substituted ferrimagnetic yttrium iron garnet thin film with linearly polarized 100 fs laser pulses triggers large-angle magnetization precession with an amplitude, phase, and frequency determined by the characteristics of the laser pulse. The precession results from a light-induced anisotropy field with a characteristic lifetime of 20 ps, the direction of which is determined by the polarization of the light. Its strength for a pump intensity of 25 mJ/cm² is 250 G which is comparable to the intrinsic anisotropy of the sample. By choosing the proper laser-pulse parameters, we were able to excite a precession with an amplitude as large as 20^∘ and a precession frequency modified by up to 50%.