We investigated spin-dependent transport properties in CoFe/MgO/n+-Si junctions by measuring Hanle signals and their dependence on the measurement frequency. The CoFe/MgO/n+-Si junctions exhibited two types of Hanle curves with different half-widths. Hanle signals with a broad half-width were observed mainly in the low-bias region, and these signals exhibited apparent frequency dependence and disappeared in the highfrequency region though Hanle signals with narrow half-widths were almost independent of the measurement frequency used in this study. This frequency dependence is explained by the mechanism of two-step tunneling. These results show that investigating the frequency response signals gives clear information on spin-dependent transport mechanisms.
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