Long electron spin memory times in gallium arsenide

Extremely long electron spin memory times in GaAs are reported. It was established by the optical orientation method that the spin relaxation time of electrons localized at shallow donors in $n$-type gallium arsenide $(N_d-N_A\approx10^{14}\,$cm$^{-3}$) is $290\pm30\,$ ns at a temperature of $4.2$ K. The exchange interaction of quasi-free electrons and electrons at donors suppresses the main spin-loss channel for electrons localized at donors-spin relaxation due to the hyperfine interaction with lattice nuclei.