Critical effect of spin-dependent transport in a tunnel barrier on enhanced Hanle-type signals observed in three-terminal geometry

The MgO thickness dependence of Hanle signals in Co50Fe50/MgO/n-Si tunnel junctions was investigated using a three-terminal geometry. The observed Hanle signal is several orders of magnitude stronger than the predicted value by conventional theory as reported in many literatures. Furthermore, the magnitude of the spin signal depends on the junction resistance rather than the channel resistance, implying that the largest part of the observed Hanle signal is not caused by spin accumulation in the semiconductor region. A possible origin of the observed strong Hanle signal is due to a modulation of the tunneling resistance by a magnetic field, which is induced by the spin precession in localized states formed in the vicinity of the Co50Fe50/MgO interface.