  The spin degree of freedom in solids offers opportunities beyond charge-based
electronics and is actively investigated for both spintronics and quantum
computation. However, the interplay of these spins with their native
environment can give rise to detrimental effects such as spin relaxation and
decoherence. Here, we use an all-electrical, lateral GaAs spin valve to
manipulate and investigate the inherent nuclear spin system. Hanle satellites
are used to determine the nuclear spin relaxation rates for the previously
unexplored temperature range down to 100 mK, giving T1 times as long as 3
hours. Despite metallic temperature dependence of resistivity, the observed
relaxation rates show a sub-linear temperature dependence. This contrasts the
Korringa relaxation mechanism observed in metals but is not inconsistent with
hyperfine-mediated relaxation in a disordered, interacting conductor not far
from the metal-insulator transition. We discuss possible relaxation mechanisms
and further investigate inhomogeneities in the nuclear spin polarization.
