Heat generation by electric current, which is ubiquitous in electronic devices and circuits, raises energy consumption and will become increasingly problematic in future generations of high-density electronics. The control and re-use of heat are therefore important topics for existing and emerging technologies, including spintronics. Recently it was reported that heat flow within a ferromagnet can produce a flow of spin angular momentum-a spin current-and an associated voltage. This spin Seebeck effect has been observed in metallic, insulating and semiconductor ferromagnets with temperature gradients across them. Here we describe and report the demonstration of Seebeck spin tunnelling-a distinctly different thermal spin flow, of purely interfacial nature-generated in a tunnel contact between electrodes of different temperatures when at least one of the electrodes is a ferromagnet. The Seebeck spin current is governed by the energy derivative of the tunnel spin polarization. By exploiting this in ferromagnet-oxide-silicon tunnel junctions, we observe thermal transfer of spins from the ferromagnet to the silicon without a net tunnel charge current. The induced spin accumulation scales linearly with heating power and changes sign when the temperature differential is reversed. This thermal spin current can be used by itself, or in combination with electrical spin injection, to increase device efficiency. The results highlight the engineering of heat transport in spintronic devices and facilitate the functional use of heat.

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ResiScope mapping showing the strong reduction of resistance induced by a graphene sheet inserted between silicon and gold.

Due to the difficulty to grow high quality semiconductors on ferromagnetic metals, the study of spin diffusion transport in Si was only limited to lateral geometry devices. In this work, by using ultrahigh vacuum wafer-bonding technique, we have successfully fabricated metal-semiconductor-metal CoFeB/MgO/Si/Pt vertical structures. We hereby demonstrate pure spin-current injection and transport in the perpendicular current flow geometry over a distance larger than 2µm in n-type Si at room temperature. In those experiments, a pure propagating spin-current is generated via ferromagnetic resonance spin-pumping and converted into a measurable voltage by using the inverse spin-Hall effect occurring in the top Pt layer. A systematic study by varying both Si and MgO thicknesses reveals the important role played by the localized states at the MgO/Si interface for the spin-current generation.Proximity effects involving indirect exchange interactions between the ferromagnet and the MgO/Si 2 interface states appears to be a prerequisite to establish the necessary out-of-equilibrium spin-population in Si under the spin-pumping action.