Electrical detection of dynamic nuclear polarization and nuclear magnetic resonance in ferromagnet-semiconductor heterostructures*

We report all-electrical measurements of dynamic nuclear polarization (DNP) and nuclear magnetic resonance (NMR) in ferromagnet-semiconductor heterostructures. Nuclei in GaAs are polarized by electron spins injected through an epitaxial Fe/GaAs Schottky tunnel barrier. In an oblique Hanle geometry, electron spin depolarization due to the hyperfine field is detected by measuring the change in spin-dependent electrochemical potential with a Fe contact.We also report electrical measurements of both magnetic and current driven NMR. A transverse magnetic field or the injection current is modulated at the NMR frequency to suppress DNP, resulting in changes of up to 80{\%} in the spin-dependent voltage. We measured resonant frequencies of different isotopes in the GaAs channel. Harmonics of the fundamental transitions are observed, reflecting the existence of either quadrupolar coupling or dipole-dipole interactions.