First-principles calculations for transient absorption of laser-excited magnetic materials

We investigate the modification in the optical properties of laser-excited bulk cobalt and nickel using the time-dependent density functional theory at a finite electron temperature. As a result of the first-principles simulation, a complex change in the photoabsorption of the magnetic materials is observed around the $M_{2,3}$ absorption edge. Based on the microscopic analysis, we clarify that this complex absorption change consists of the two following components: (i) the decrease in the photoabsorption in a narrow energy range around the $M_{2,3}$ edge, which reflects the blue shift of the absorption edge due to the light-induced demagnetization, and (ii) the increase in the photoabsorption in a wider range around the $M_{2,3}$ edge, which reflects the modification in the local-field effect due to the light-induced electron localization. The relation between the transient optical and magnetic properties may open a way to monitor ultrafast (de)magnetization and spin dynamics in magnetic materials via transient absorption spectroscopy.