Spin-dependent photoelectron tunneling from GaAs into magnetic cobalt

The spin dependence of the photoelectron tunnel current from free-standing GaAs films into out-of-plane magnetized cobalt films is demonstrated. The measured spin asymmetry (A), resulting from a change in light helicity, reaches ±6% around zero applied tunnel bias and drops to ±2% at a bias of -1.6V applied to the GaAs. This decrease is a result of the drop in the photoelectron-spin polarization that results from a reduction in the GaAs surface-recombination velocity. The sign of A changes with that of the cobalt magnetization. In contrast, A is negligible on nonmagnetic gold films.