Electron spin dynamics and hyperfine interactions in Fe Al0.1Ga0.9As GaAs spin injection heterostructures

We have completed a comprehensive study of hyperfine interactions between spin-polarized electrons and lattice nuclei in Al0.1Ga0.9As GaAs quantum well (QW) heterostructures. The spin-polarized electrons are electrically injected into the semiconductor heterostructure from a metallic ferromagnet across a Schottky tunnel barrier. The nuclear polarization and electron spin dynamics are accurately modeled using the formalism developed previously for optical orientation in GaAs. We find that the nuclear spin polarization in the QW is directly proportional to the electron spin polarization but depends only weakly on the electron density in the QW. The direction of the nuclear spin polarization can be controlled by the reversal of the magnetization in the ferromagnet. Nuclear magnetic resonance (NMR) is observed at low applied magnetic fields by electrically modulating the spin injected into the QW. The electrically driven NMR demonstrates explicitly the existence of a Knight field felt by the nuclei due to the electron spin as well as the presence of significant dipolar coupling between nuclei.