Exchange-driven spin relaxation in ferromagnet/oxide/semiconductor heterostructures

We investigate electron spin relaxation in GaAs in the proximity of a Fe/MgO layer using spin-resolved optical pump-probe spectroscopy, revealing a strong dependence of the spin relaxation time on the strength of an exchange-driven hyperfine field. The temperature dependence of this effect reveals a strong correlation with carrier freeze out, implying that at low temperatures the free carrier spin lifetime is dominated by inhomogeneity in the local hyperfine field due to carrier localization. This result resolves a long-standing and contentious question of the origin of the spin relaxation in GaAs at low temperature when a magnetic field is present. Further, this improved fundamental understanding paves the way for future experiments exploring the time-dependent exchange interaction at the ferromagnet/semiconductor interface and its impact on spin dissipation and transport in the regime of dynamically-driven spin pumping.