Spin relaxation of conduction electrons inAlxGa1−xAs

We report measurements of conduction-electron spin relaxation times $T_1$ in ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ ($0.07\le x\le 0.28$) ($4.7\le T\le 300$ K) using optical spin-orientation techniques. $T_1$ above about 50 K is strongly temperature dependent, and its order of magnitude and temperature dependence may be accounted for by the D'yakanov-Perel mechanism, in which band-structure-induced spin relaxation is strongly narrowed by momentum relaxation. We estimate that the Elliott mechanism is, however, only one order of magnitude weaker, and it cannot be completely ruled out. At temperatures below about 50 K, $T_1$ is limited by nuclear hyperfine effects.