Ultrafast Light-Induced Magnetization Dynamics of Ferromagnetic Semiconductors

We develop a theory of ultrafast light-induced magnetization dynamics in ferromagnetic semiconductors. We demonstrate magnetization control during femtosecond time scales via the interplay between nonlinear circularly polarized optical excitation, hole-spin damping, polarization dephasing, and Mn-hole-spin interactions. Our results show magnetization relaxation and precession for the duration of the optical pulse governed by the nonlinear optical polarizations and populations.

Figure 1

Dependence of Mn-spin trajectory on the relaxation: (a) $T_2=2T_1=330\mathrm{fs}$, ${\Gamma }_s=0$ (coherent limit); (b) $T_2=2T_1=330\mathrm{fs}$, $1/{\Gamma }_s=10.5\mathrm{fs}$; (c) $T_1=165\mathrm{fs}$, $T_2=1/{\Gamma }_s=10.5\mathrm{fs}$.

Figure 2

Trajectories of the light-induced field $\mathbf{h}$ (units of $d(0)/2E_F$) for the three relaxation regimes of Fig. 1.