We demonstrated electrical spin injection from a half-metallic Heusler alloy Co 2 MnSi electrode into a GaAs channel through observation of a spin-valve signal and a Hanle signal in the four-terminal nonlocal geometry. Furthermore, we electrically detected a nuclear field acting on electron spins, which was produced by the dynamic nuclear polarization, through observation of transient oblique Hanle signals. Samples with a Co 2 MnSi spin source exhibited higher spin-injection efficiency and a

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... ger nuclear field compared to samples with a Co 50 Fe 50 spin source, suggesting that the spin polarization of Co 2 MnSi is higher. This higher polarization is promising for realizing future spintronic devices and for understanding spin interactions as well as spin-dependent transport properties in a semiconductor channel.