Proximity exchange coupling across an MgO tunnel barrier is observed up to room temperature. The proximity exchange field, which ferromagnetic Fe exerts on the spin accumulation in a Fe/MgO/Si tunnel contact, modifies the spin precession of the spin accumulation at the MgO/Si interface and is detected via the inverted Hanle effect in a three-terminal configuration. It produces shifts and hysteresis of the inverted Hanle curves, and discontinuities at the coercive field of the ferromagnet, at which the magnetization and thereby the exchange field is reversed. The proximity exchange field is observed not only at low temperature, as we previously reported, but also at room temperature. We compare the magnitude of the exchange field at different temperatures, and complement this with data on the tunnel resistance and the tunnel spin polarization, which was extracted from four-terminal non-local spin transport in the same devices.
The electrical injection, transport and detection of spins in silicon is studied using non-local spin-transport devices with an n-type Si channel and Fe/MgO magnetic tunnel contacts. Clear spin-valve and Hanle spin signals with consistent magnitude are observed, unambiguously proving the existence of a spin accumulation in the Si channel. Importantly, the spin accumulation is very large, and increased by one to two orders of magnitude when compared to previous reports. We attribute this to the large tunnel spin polarization of the Fe/MgO contacts. Using devices with different growth procedures it is shown that the quality of the tunnel contacts and the magnitude of the non-local spin signals depend significantly on the details of the contact fabrication. The results demonstrate that a large spin accumulation can indeed be induced in Si, as is required for the development of Si spintronic devices with a large magnetic response.
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