Photoinduced demagnetization and its dynamical behavior in a (Nd_0.5Sm_0.5)_0.6Sr_0.4MnO₃ thin film

We have observed a significant change of absorption spectrum in the visible region by the irradiation of an intense laser pulse in a double-exchange ferromagnet (Nd_0.5Sm_0.5)_1-xSr_xMnO₃ (x=0.4) thin film. In the ferromagnetic state, the increase of spectral weight of the interband transition between J-split bands has been observed, indicating that the photoexcited e_g carriers suppress the neighboring spin correlation. The time-resolved spectroscopy in a vast time domain from 100 fs to 1 μs has shown that the photoinduced demagnetization occurs within 200 ps after the photoinjection and spin correlation recovers in 300 ns. We further found that the demagnetization efficiency strongly depends on the spin direction of the excited e_g carriers.