Giant Spin Accumulation in Silicon Nonlocal Spin-Transport Devices

Abstract

Although the electrical injection, transport and detection of spins in silicon have been achieved, the induced spin accumulation was much smaller than expected and desired, limiting the potential impact of Si-based spintronic devices. Here, using non-local spin-transport devices with an n-type Si channel and Fe/MgO magnetic tunnel contacts, we demonstrate that it is possible to create a giant spin accumulation in Si, with the spin splitting reaching 13 meV at 10 K and 3.5 meV at room temperature. The non-local spin signals are in good agreement with a numerical evaluation of spin injection and diffusion that explicitly takes the size of the injector contact into account. The giant spin accumulation originates from the large tunnel spin polarization of the Fe/MgO contacts (53 % at 10 K and 18 % at 300 K), and the spin density enhancement achieved by using a spin injector with a size comparable to the spin-diffusion length of the Si. The ability to induce a giant spin accumulation enables the development of Si spintronic devices with a large magnetic response.

Nonlinear Electrical Spin Conversion in a Biased Ferromagnetic Tunnel Contact

“…In the so-called nonlocal spin transport devices 19,20 , one employs a four-terminal measurement configuration in which one ferromagnetic contact is biased in order to induce a spin accumulation in the nonmagnetic channel, whereas the second ferromagnetic contact, the spin detector, remains unbiased. The spin signals observed in such nonlocal devices with tunnel contacts [21][22][23][24][25][26][27][28][29] are well described by the theory for spin injection and detection in the linear response regime 13,30 . Consequently, nonlocal devices have been instrumental to prove and understand spin injection and transport in a wide variety of materials, although they are of little direct technological relevance.…”

Spin injection through energy-band symmetry matching with high spin polarization in atomically controlled ferromagnet/ferromagnet/semiconductor structures

“…Therefore, spin injection technique with a band symmetry-matched CFAS/Fe/Ge(111) heterostructure is available for achieving high-performance SC-based spintronic devices even at room temperature. If energy-band symmetry matching without the use of insulator barrier layers is proposed and developed for other semiconducting channel materials, such as Si 3,7,34 and graphene 35,36 , then efficient spin injection techniques can be utilized even for other group IV SC spintronic devices that can operate at room temperature. This approach provides a new solution for the simultaneous achievement of a high MR ratio and a low parasitic resistance in future SC spintronic architectures at room temperature.…”

“…To date, the introduction of tunnel barriers between FMs and SCs has been generally proposed to eliminate the large conductivity mismatch between FMs and SCs 5,6 . High output voltages derived from the large spin accumulation in Si were recently demonstrated in FM/MgO/Si lateral devices at room temperature 7,8 . If a two-terminal magnetoresistance (MR) ratio, which is the most important performance measure of a nonvolatile memory, of more than 100% can be obtained at room temperature even in metaloxide-semiconductor field-effect-transistor structures, then one can effectively utilize the spin-related phenomena in high-performance applications of SC architectures 9 .…”

Effects of screened Coulomb interaction on spin transfer torque

“…The third term is the spin-dependent energy shift due to spin accumulation µ. In magnetic multilayer, there is a spin accumulation on the nearly magnetic metal that accommodates non-local spin transfer [20,21]. The last term is the s-d exchange interaction of conduction electron with localized spin…”