We study electron-spin relaxation induced by Mn spins and effects of LO-phonon scattering in CdMnTe quantum wells, where Mn contents of 3.6 and 5.0 at% are examined. By using pump-probe absorption a under magnetic field, the time constant of the electron-spin relaxation Τe is deduced as a function of the magnetic field. Values of Τe under magnetic fields are five times different between both the Mn contents, while those at 0 T reflect the Mn content. The latter fact for the spin-relaxation times at 0 T shows that the electron-spin relaxation is induced by Mn spins via the s-d exchange interaction. However, the former significant difference in Τe suggests that the number of effective Mn spins involved in the electron-energy relaxation is greatly different in the spin-relaxation between the spin-splitting electron levels under different magnetic fields. The effects of LO-phonon scattering on the electron-spin relaxation are observed when the spin-splitting is close to the one-LO-phonon energy, indicating an effective path of the electron-spin relaxation involving both the LO phonon and the Mn spins.
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