We report on a study of the spin coherence and on the formation dynamics of charged excitons in a p-doped CdTe/Cd 1ϪxϪy Mg x Zn y Te quantum well by time-resolved photoluminescence under strictly resonant excitation of either the neutral or the charged exciton transition. The analysis of the decay of the charged exciton photoluminescence polarization and of the oscillation of this polarization when a transverse magnetic field is applied allows us to conclude that the formation of a charged exciton via an exciton state does not affect either the electron spin orientation or its coherence. The radiative lifetime of the charged exciton is directly measured and is found to be ϳ60 ps. Its formation time is determined from the experiments via a detailed model and is found to be ϳ65 ps. We also obtain information on the excitonic spin-flip time ͑12 ps͒ and the single-carrier spin-flip times within the exciton ͑electron, 60 ps and hole, 20 ps͒.
In this letter, magnetization reversal is investigated in (Ga,Mn)As thin films using the magneto-optical Kerr effect. A Stoner–Wohlfart model, modified to take into account the existence of magnetic reversal discontinuities associated with nucleation and propagation phenomena allows us to estimate most of the characteristic constants. These results demonstrate a reversal behavior analogous to that observed in metallic magnetic layers (coherent rotation followed by a nucleation propagation process). The dynamic study at T=20 K shows a strong increase of the coercivity with the increase of dH/dt. This effect is related to the random distribution of Mn magnetic ions in the lattice.
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