Low-temperature spin relaxation in n-type GaAs
  Low-temperature electron spin relaxation is studied by the optical orientation method in bulk n-GaAs with donor concentrations from 10^14 cm^{-3} to 5x10^17 cm^{-3}.   A peculiarity related to the metal-to-insulator transition (MIT) is observed in the dependence of the spin lifetime on doping near n_D = 2x10^16 cm^{-3}. In the metallic phase, spin relaxation is governed by the Dyakonov-Perel mechanism, while in the insulator phase it is due to anisotropic exchange interaction and hyperfine interaction 
R.I. Dzhioev, K.V. Kavokin, V.L. Korenev, M.V. Lazarev, B.Ya. Meltser,   M.N. Stepanova, B.P. Zakharchenya, D. Gammon, D.S. ...