Spin relaxation near a ferromagnetic transition

We study spin relaxation in dilute magnetic semiconductors near a ferromagnetic transition, where spin fluctuations become strong. An enhancement in the scattering rate of itinerant carriers from the spin fluctuations of localized impurities leads to a change in the dominant spin relaxation mechanism from Dyakonov-Perel to spin flips in scattering. On the ferromagnetic side of the transition, we show that due to the presence of two magnetic components -- the itinerant carriers and the magnetic impurities -- with different gyromagnetic ratios, the relaxation rate of the total magnetization can be quite different from the relaxation rate of the spin. Following a disturbance of the equilibrium magnetization, the spin is initially redistributed between the two components to restore the equilibrium magnetization. It is only on a longer time scale, controlled by the spin-orbit interaction, that the total spin itself relaxes to its equilibrium state.

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