  Spin injection in high-quality epitaxial Mn5Ge3 Schottky contacts on n-type
Ge has been investigated using a three-terminal Hanle effect measurement. Clear
Hanle and inverted Hanle signals with features characteristic of spin
accumulation and spin precession are observed up to 200 K. Strikingly, the
observed spin voltage is several orders of magnitude larger than predicted by
the theory of spin injection and diffusive spin transport. Since the devices
have no oxide tunnel barrier, the discrepancy between theory and experiments
cannot be explained by the often-invoked spin accumulation in localized states
associated with the oxide or oxide/semiconductor interface. The observed spin
voltages therefore must originate from the Ge itself, either from spins in the
Ge bulk bands or its depletion region.
