Dynamics of magnetic-polaron formation in ${\mathrm{Cd}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Se and ${\mathrm{Cd}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Te

Evidence that magnetic polarons are formed via electron mediated ${\mathrm{Mn}}^{2+}$ spin diffusion in ${\mathrm{Cd}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Mn}}_{\mathrm{x}}$Se (x=0.05, 0.10, 0.20, 0.30) and ${\mathrm{Cd}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Mn}}_{\mathrm{x}}$Te (x=0.20, 0.30, 0.45) has been obtained from picosecond time-resolved photoluminescence experiments. The time-varying Stokes shift in the luminescence energy of the exciton associated with the magnetic polaron is measured to obtain the magnetic-polaron formation time. The formation time is observed to increase linearly with temperature (T=1.8 to 90 K) and quadratically with applied magnetic field (B=0 to 90 kG). These results are in agreement with a spin-diffusion model of magnetic-polaron formation described here.