We demonstrate electrical injection and detection of spin-polarized electrons in silicon (Si) using epitaxially grown ${\text{Fe}}_3\text{Si}/\text{Si}$ Schottky-tunnel-barrier contacts. By an insertion of a $\delta$ -doped $n^{+}\text{-Si}$ layer $\left(\sim {10}^{19}{\text{cm}}^{-3}\right)$ near the interface between a ferromagnetic ${\text{Fe}}_3\text{Si}$ contact and a Si channel $\left(\sim {10}^{15}{\text{cm}}^{-3}\right)$ , we achieve a marked enhancement in the tunnel conductance for reverse-bias characteristics of the ${\text{Fe}}_3\text{Si}/\text{Si}$ Schottky diodes. Using laterally fabricated four-probe geometries with the modified ${\text{Fe}}_3\text{Si}/\text{Si}$ contacts, we detect nonlocal output signals that originate from the spin accumulation in a Si channel at low temperatures.

The generation, manipulation and detection of a pure spin current (i.e., the flow of spin angular momentum without a charge current) are prospective approaches for realizing next-generation spintronic devices with ultra-low electric power consumption. Conventional ferromagnetic electrodes such as Co and NiFe have been utilized as spin injectors to generate pure spin currents in nonmagnetic channels. However, the generation efficiency of pure spin currents is extremely low at room temperature, giving rise to a serious obstacle for device applications. Here we demonstrate the generation of giant pure spin currents at room temperature in lateral spin valve devices with a highly ordered Heusler-compound Co₂FeSi (CFS) spin injector. The generation efficiency of pure spin currents from the CFS spin injectors is 10 times greater than that of the NiFe injectors, indicating that Heusler compound spin injectors with high spin polarization enable us to materialize a high-performance lateral spin device. The present study is a technological jump in spintronics, and indicates the great potential of ferromagnetic Heusler compounds with half metallicity for generating pure spin currents.

For the study of ferromagnetic materials which are compatible with group-IV semiconductor spintronics, we demonstrate control of the ferromagnetic properties of Heusler-alloy ${\mathrm{Fe}}_{3-x}{\mathrm{Mn}}_x\mathrm{Si}$ epitaxially grown on Ge(111) by tuning the Mn composition $x$. Interestingly, we obtain $L{2}_1$-ordered structures even for nonstoichiometric atomic compositions. The Curie temperature of the epilayers with $x\approx 0.6$ exceeds 300 K. Theoretical calculations indicate that the electronic structures of the nonstoichiometric ${\mathrm{Fe}}_{3-x}{\mathrm{Mn}}_x\mathrm{Si}$ alloys become half-metallic for $0.75\le x\le 1.5$. We discuss the possibility of room-temperature ferromagnetic ${\mathrm{Fe}}_{3-x}{\mathrm{Mn}}_x\mathrm{Si}/\mathrm{Ge}$ epilayers with high spin polarization.

The authors have fabricated a lateral double barrier magnetic tunnel junction (MTJ) which consists of a single self-assembled InAs quantum dot (QD) with ferromagnetic Co leads. The MTJ shows clear hysteretic tunnel magnetoresistance (TMR) effect, which is evidence for spin transport through a single semiconductor QD. The TMR ratio and the curve shapes are varied by changing the gate voltage.

We study room-temperature generation and detection of pure spin currents using lateral spin-valve devices with electrodes formed from the Heusler compounds Co${}_2$FeSi (CFS) or Fe${}_3$Si (FS). The magnitude of the nonlocal spin-valve signals is strongly affected by resistivity variations observed particularly in low-temperature-grown Heusler compounds containing ordered structures. From an analysis based on a one-dimensional spin diffusion model, we find that the spin polarization monotonically increases with decreasing resistivity, which depends on the structural ordering, for both the CFS and FS electrodes, and show that CFS has a larger spin polarization than FS.

To develop silicon-based spintronic devices, we have explored high-quality ferromagnetic ${\mathrm{Fe}}_3\mathrm{Si}$ /silicon (Si) structures. Using low-temperature molecular beam epitaxy at $130°\mathrm{C}$ , we realize the epitaxial growth of ferromagnetic ${\mathrm{Fe}}_3\mathrm{Si}$ layers on Si(111) with an abrupt interface, and the grown ${\mathrm{Fe}}_3\mathrm{Si}$ layer has the ordered $D{O}_3$ phase. Measurements of magnetic and electrical properties for the ${\mathrm{Fe}}_3\mathrm{Si}∕\mathrm{Si}\left(111\right)$ yield a magnetic moment of $\sim 3.16{\mu }_B∕\mathrm{f.u.}$ at room temperature and a rectifying Schottky-diode behavior with the ideality factor of $\sim 1.08$ , respectively.