RESUMEN
Due to the difficulty of growing high-quality semiconductors on ferromagnetic metals, the study of spin diffusion transport in Si was limited to lateral geometry devices. In this work, by using an 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 2 µm 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 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 interface states appears to be a prerequisite to establishing the necessary out-of-equilibrium spin population in Si under the spin-pumping action.
RESUMEN
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.
RESUMEN
Integrating tunneling magnetoresistance (TMR) effect in memristors is a long-term aspiration because it allows to realize multifunctional devices, such as multi-state memory and tunable plasticity for synaptic function. However, the reported TMR in different multiferroic tunnel junctions is limited to 100%. This work demonstrates a giant TMR of -266% in La0.6Sr0.4MnO3(LSMO)/poly(vinylidene fluoride)(PVDF)/Co memristor with thin organic barrier. Different from the ferroelectricity-based memristors, this work discovers that the voltage-driven florine (F) motion in the junction generates a huge reversible resistivity change up to 106% with nanosecond (ns) timescale. Removing F from PVDF layer suppresses the dipole field in the tunneling barrier, thereby significantly enhances the TMR. Furthermore, the TMR can be tuned by different polarizing voltage due to the strong modification of spin-polarization at the LSMO/PVDF interface upon F doping. Combining of high TMR in the organic memristor paves the way to develop high-performance multifunctional devices for storage and neuromorphic applications.
RESUMEN
The interface resistance at metal/semiconductor junctions has been a key issue for decades. The control of this resistance is dependent on the possibility to tune the Schottky barrier height. However, Fermi level pinning in these systems forbids a total control over interface resistance. The introduction of 2D crystals between semiconductor surfaces and metals may be an interesting route towards this goal. In this work, we study the influence of the introduction of a graphene monolayer between a metal and silicon on the Schottky barrier height. We used X-ray photoemission spectroscopy to rule out the presence of oxides at the interface, the absence of pinning of the Fermi level and the strong reduction of the Schottky barrier height. We then performed a multiscale transport analysis to determine the transport mechanism. The consistency in the measured barrier height at different scales confirms the good quality of our junctions and the role of graphene in the drastic reduction of the barrier height.