Photoinduced Spin Disorder in Half-Metal CrO₂ films

We investigate the photoinduced effects on the spin state for half-metallic ferromagnet CrO₂ (T_C～390K), in which the conducting electrons are totally polarized, by means of the time-resolved pump--probe method at the temperature range from 300K to 470K. A significant negative change ΔT/T for the transmittance spectrum at 1.55eV under photo-excitation is found. The ΔT/T value monotonically decreases on approaching to T_C from the low temperature side, suggesting a photoinduced spin disorder state. Furthermore, we calculate the saturation magnetization M_S of CrO₂ in both the ground and photo-excited states by using the local-spin-density approximation plus U (LSDA+U) method, and find a decrease of the M_S-value in the photo-excited state. The suppressed M_S-value in the photo-excited state is consistent with the experimental data.