Larmor precession of Mn2+ moments initiated by the exchange field of photoinjected carriers in CdTe/Cd1-xMnxTe quantum wells

We observed dynamical processes of the magnetic moments of photoinjected carriers and resultant perturbed magnetic moment of Mn2+ ions in CdTe/Cd1-xMnxTe quantum wells by means of the femtosecond time-resolved magneto-optical Kerr rotation measurement in transverse magnetic fields. The time-resolved Kerr rotation signal shows that the Larmor precession of Mn2+ moment is initiated by photoinjected carriers. In particular, we observed a time delay in terms of the phase and an amplitude of Mn2+ beats as a function of the external field to confirm the mechanism of perturbing the Mn2+ moment, i.e., a transient p-d exchange field, proposed in earlier studies. The motion of the Mn2+ moment is also simulated by the Bloch model including the impulsive transverse exchange fields produced by the conduction electron and heavy-hole spins. From this it is found that the exchange field of the heavy-hole spin contributes dominantly to tipping the Mn2+ moment away from the external field axis. The exchange field estimated by the Bloch model so as to fit experimental data is in reasonable agreement with the exchange field estimated from p-d exchange interaction, which also supports the above mechanism.