To develop silicon-based spintronic devices, we have explored high-quality ferromagnetic Fe3Si/silicon (Si) structures. Using low-temperature molecular beam epitaxy at 130 • C, we realize epitaxial growth of ferromagnetic Fe3Si layers on Si (111) with keeping an abrupt interface, and the grown Fe3Si layer has the ordered DO3 phase. Measurements of magnetic and electrical properties for the Fe3Si/Si(111) yield a magnetic moment of ∼ 3.16 µB/f.u. at room temperature and a rectifying Schottky-diode behavior with the ideality factor of ∼ 1.08, respectively. PACS numbers:Semiconductor spintronic devices such as spin-field effect transistors (spin FET) are one of the possible candidates to substitute for existing silicon-based complementary metal-oxide-semiconductor devices. [1,2,3,4] To realize operations of the spin FET, an electrical spin injection from ferromagnets into semiconductors is an essential technology. For III-V semiconductor devices, several groups have demonstrated highly efficient spin injection and detection using an epitaxial Fe thin film and tailored Schottky tunnel barriers so far. [5,6,7] From these facts, it is necessary for semiconductor spintronics to develop crystal growth techniques of ferromagnets on semiconductors with keeping high-quality interfaces. In particular, it will become key to build epitaxial growth of ferromagnets on silicon (Si) from the viewpoint of application to existing silicon large-scale integrated circuit (LSI) technologies. [8] Moreover, for spintronics, Si has been regarded as an ideal material because of a long spin relaxation time due to weak spin-orbit interaction, weak hyperfine interaction and lattice inversion symmetry, which will give rise to a long spin diffusion length in the devices. Recently, spin transport in Si conduction channels was experimentally demonstrated although their operations were limited at low temperatures. [9,10,11] This means that the spin degree of freedom can be introduced into Si-based electronic devices.To date, ferromagnetic MnAs thin films have been grown epitaxially on Si (001), [12] but electrical spin injection from MnAs into Si across a Schottky tunnel barrier has never been demonstrated unfortunately. Also, the Curie temperature of MnAs is ∼ 315 K, [13] which may be relatively low for an operation temperature of future LSIs. Thus, possibilities of other high-Curie temperature materials compatible with Si should be explored. Here we select a ferromagnetic Heusler alloy Fe 3 Si thin film, which has a high Curie temperature above 800 K, a relatively high spin polarization of ∼ 45 % and a small coercive field of ∼ 7.5 Oe. [14] In this letter, we achieve highly

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 Co 2 FeSi (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.

We demonstrate electrical injection and detection of spin-polarized electrons in silicon (Si) using epitaxially grown Fe3Si/Si Schottky-tunnel-barrier contacts. By an insertion of a δ-doped n + -Si layer (∼ 10 19 cm −3 ) near the interface between a ferromagnetic Fe3Si contact and a Si channel (∼ 10 15 cm −3 ), we achieve a marked enhancement in the tunnel conductance for reverse-bias characteristics of the Fe3Si/Si Schottky diodes. Using laterally fabricated four-probe geometries with the modified Fe3Si/Si contacts, we detect nonlocal output signals which originate from the spin accumulation in a Si channel at low temperatures. PACS numbers:To solve critical issues caused by the scaling limit of complementary metal-oxide-semiconductor (CMOS) technologies, spin-based electronics (spintronics) has been studied.[1] For semiconductor spintronic applications, an electrical spin injection from a ferromagnet (FM) into a semiconductor (SC) and its detection are crucial techniques.Recently, methods for spin injection and/or detection in silicon (Si) were explored intensely [2,3,4,5,6,7] because Si has a long spin relaxation time and is compatible with the current industrial semiconductor technologies. Although electrical detections of spin transport in Si conduction channels were demonstrated by two research groups, [4,5] an insulating Al 2 O 3 tunnel barrier between FM and Si was utilized for efficient spin injection and/or detection. To realize gate-tunable spin devices, e.g., spin metal-oxidesemiconductor field effect transistors (spin MOSFET), [8] demonstrations of electrical spin injection and detection in Si conduction channels using Schottky tunnel-barrier contacts will become considerably important. [9,10] By low-temperature molecular beam epitaxy (LTMBE), we recently demonstrated highly epitaxial growth of a binary Heusler alloy Fe 3 Si on Si and obtained an atomically abrupt heterointerface. [11] In this letter, inserting a heavily doped n + -Si layer near the abrupt interface between Fe 3 Si and n-Si, we achieve an effective Shottky tunnel barrier for spin injection into Si. Using nonlocal signal measurements, we demonstrate electrical injection and detection of spin-polarized electrons in Si conduction channels though the Schottky-tunnel-barrier contacts.The n + -Si layer was formed on n-Si(111) (n ∼ 4.5 × 10 15 cm −3 ) by a combination of the Si solid-phase epitaxy with an Sb δ-doping process, [12] where the carrier * E-mail: hamaya@ed.kyushu-u.ac.jp † E-mail: miyao@ed.kyushu-u.ac.jp concentration of the n + -Si layer was ∼ 2.3 × 10 19 cm −3 , determined by Hall effect measurements, and ∼ 10-nmthick non-doped Si layer was grown on the Sb δ-doped layer. Ferromagnetic Fe 3 Si layers with a thickness of ∼ 50 nm were grown by LTMBE at 130 • C, as shown in our previous work.[11] The interface between Fe 3 Si and n + -Si was comparable to that shown in Ref. 11. To evaluate electrical properties of the Fe 3 Si/Si Schottky contacts, we firstly fabricated two different Schottky diodes (∼ 1 mm in diameter) with and w...

We 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. PACS numbers:The research field of semiconductor-based spin electronics (spintronics) has opened up a new technology for spin manipulation by means other than magnetic field.[1, 2] For developing semiconductor nanospintronic applications and discovering novel physical phenomena, one is extremely interested in technological possibilities for spin injection into a single semiconductor quantum dot (QD) which behaves as an artificial atom.[3] To date, many theoretical studies of spin transport through a single nonmagnetic island with ferromagnetic leads have been reported, [4,5,6,7,8,9] and spin accumulation in the island was predicted in their reports. Very recently, for metallic systems, spin injection into a single nonmagnetic nanoparticle was achieved,[10] which indicates the occurrence of spin accumulation. For an individual carbon nanotube (CNT) with ferromagnetic leads, the spin transport [11,12] and its gate-control [13,14,15,16] have also been demonstrated, showing possible spintronic applications using CNTs. However, no experimental work on spin-dependent transport through a single semiconductor QD has been reported yet.Recently, Jung et al. [17] succeeded in transport measurements for a single self-assembled InAs QD in contact with nonmagnetic leads and clearly observed shell structures due to an artificial atomic nature. Replacing the nonmagnetic leads with ferromagnetic ones, we

We study electrical properties of metal/Ge contacts with an atomically controlled interface, and compare them with those with a disordered one, where atomically controlled interfaces can be demonstrated by using Fe3Si/Ge(111) contacts. We find that the Schottky barrier height of Fe3Si/n-Ge(111) contacts is unexpectedly lower than those induced by the strong Fermi-level pinning at other metal/n-Ge contacts. For Fe3Si/p-Ge(111) contacts, we identify clear rectifying behavior in I-V characteristics at low temperatures, which is also different from I-V features due to the strong Fermi-level pinning at other metal/p-Ge contacts. These results indicate that there is an extrinsic contribution such as dangling bonds to the Fermi-level pinning effect at the directly connected metal/Ge contacts.

We study the electrical detection of spin accumulation at a ferromagnet-silicon interface, which can be verified by measuring a Hanle effect in three-terminal lateral devices. The device structures used consist of a semiconducting Si channel and a Schottky tunnel contact. In a low currentbias region, the Hanle-effect curves are observed only under forward bias conditions. This can be considered that the electrical detectability at the forward-biased contact is higher than that at the reverse-biased contact. This is possible evidence for the detection of spin-polarized electrons created in a Si channel.

We study ferromagnetic properties of Heusler-alloy Co2FeSi epilayers grown on silicon (Si). The magnetic moment and in-plane magnetic anisotropy of the Co2FeSi/Si(111) epilayers vary significantly with the growth temperature (TG) even in the low-temperature region (TG≤200 °C). These features are induced by reaction phases formed at the interface between Co2FeSi and Si. At TG=100 °C, however, we can obtain both highly ordered L21 structures on Si and high-quality Co2FeSi/Si heterointerfaces at the same time. This fact will open a road to realize a Co-based half-metallic spin injector and detector for Si-based spintronic devices.

Articles you may be interested inTunneling magnetoresistance effect in a few-electron quantum-dot spin valve Appl. Phys. Lett. 93, 222107 (2008); 10.1063/1.3042098 High Kondo temperature ( T K 80 K ) in self-assembled InAs quantum dots laterally coupled to nanogap electrodes Appl. Phys. Lett. 93, 062101 (2008); 10.1063/1.2968206 Electric-field control of tunneling magnetoresistance effect in a Ni ∕ In As ∕ Ni quantum-dot spin valve Appl. Phys. Lett. 91, 022107 (2007); 10.1063/1.2759264 Kondo effect in quantum dots coupled to ferromagnetic leads: effect of noncollinear magnetization AIP Conf.