Physical Review B, Condensed matter and materials physics vol:72 issue:3
We investigate dynamical nuclear polarization in bulk GaAs by electrical spin injection from a MnSb ferromagnetic top contact using the oblique Hanle effect to examine the circular polarization of the electroluminesence in a spin-polarized light-emitting diode. Reversing the MnSb magnetization or the external field leads to a slow response of the nuclear magnetization, which is reflected in slow changes of the optical circular polarization. Applying an ac-magnetic field at the resonance frequencies of the Ga and As isotopes results in a partial destruction of the nuclear polarization. This also showed that the As-75 nuclei are only weakly polarized. We correlate this to the combination of a higher spin relaxation time of the As-75 nuclei and the relatively long electron-nucleus-interaction time. We furthermore examined the width of the zero-field dip in the Hanle curve and explain its larger size in terms of an equilibrium between nuclear spin pumping by the electrons and nuclear relaxation.