Local Spin Valve Research Articles

Spin filtering in germanium/silicon core/shell nanowires with pseudo-helical gap

Semiconductors with strong spin–orbit interactions can exhibit a helical gap with spin-momentum locking opened by a magnetic field. Such a gap is highly spin selective as a result of a topologically protected spin-momentum locking, which can be used for spin filtering. We experimentally demonstrate such a spin filtering effect in a quasi-ballistic p-type germanium/silicon core/shell nanowire (NW), which possesses a pseudo-helical gap without the application of magnetic field. Polarized hole spin injection to the NW is achieved using cobalt ferromagnetic contacts with controlled natural surface oxide on the NW as a tunnel barrier. Local and nonlocal spin valve effects are measured as the verification of polarized spin transport in the NW outside the helical gap. We electrically tune the NW into the helical gap by scanning its chemical potential with a gate. A hysteresis loop with three resistance states is observed in the local spin valve geometry, as an evidence of spin filtering in the helical gap.

Large spatial distribution of spin accumulation in wide Au channel

Non local spin valve measurements for lateral Permalloy(Py)/Au/Py spin valve devices with various Au channel widths were carried out in two viable voltage probe configurations. With increasing the channel width at a fixed channel length, the magnitude of spin valve signal (ΔR) decays for both configurations. Non-zero ΔR is observed up to 3μm in width while no spin signal is observed even narrower width of 0.7μm when the current and voltage probes are located on the same side or opposite side with respect to the current path respectively. The magnitude of ΔR is strongly affected by the location of voltage probe on both ends of the detector as well as channel width. Large spatial distribution of spin current is initiated from inhomogeneous spin injection close to the current path and can be well understood by introducing the effective channel length.

All-electrical spin injection and detection in the Co2FeSi/GaAs hybrid system in the local and non-local configuration

We demonstrate the electrical injection and detection of spin-polarized electrons in the Co2FeSi/GaAs hybrid system using lateral transport structures. Spin valve signatures and characteristic Hanle curves are observed both in the non-local and the local configuration. The comparatively large magnitude of the local spin valve signal and the high signal-to-noise ratio are attributed to the large spin polarization at the Fermi energy of Co2FeSi in the well-ordered L21 phase.

Multiple Extraction Spin Valves for Spintronic Circuits

The application of an electrical forward bias across a ferromagnet/semiconductor Schottky barrier can result in a non-equilibrium spin accumulation in the semiconductor. This mechanism is referred to as spin extraction. Like spin injection, spin extraction can also serve to generate the electron spin polarization, which is necessary for the operation of a local spin valve, i.e., a magnetoresistance device consisting of a ferromagnetic/non-magnetic/ferromagnetic hybrid structure, which exhibits an electrical resistance that depends on the relative orientation of the magnetizations of the two ferromagnetic electrodes. In such a spin extraction spin valve (SESV), a spin-polarized drift current is generated in a non-magnetic channel by spin extraction at a ferromagnetic electrode. The spin polarization influences the output current through a subsequent ferromagnetic electrode. We show how spin valve devices relying on multiple spin extraction events can be used for magneto-logic gate operation. Furthermore, we investigate the potential use of these structures as sources of highly spin-polarized drift currents.

Local spin valve effect in lateral (Ga,Mn)As/GaAs spin Esaki diode devices

We report here on a local spin valve effect observed unambiguously in lateral all-semiconductor all-electrical spin injection devices, employing p+ −(Ga,Mn)As/n+ −GaAs Esaki diode structures as spin aligning contacts. We discuss the observed local spin-valve signal as a result of the interplay between spin-transport-related contribution and the tunneling anisotropic magnetoresistance of the magnetic contacts. The magnitude of the spin-related magnetoresistance change is equal to 30 Ω which is twice the magnitude of the measured non-local signal.

Magnetoresistance of lateral semiconductor spin valves

The magnetoresistance of two terminal lateral semiconductor spin valves with respect to varying mesa size is studied. It is shown theoretically that extended regions outside the spin-current path can act as an additional source of spin-relaxation, decreasing the magnetoresistance response. From a simplified expression of magnetoresistance derived from spin-diffusion equations, we show that it is important to etch away these extended regions for devices with channel lengths much smaller than the spin-diffusion length in order to achieve maximum magnetoresistance. Preliminary experimental data on a two terminal local spin valve are in good agreement with the theory established in this article.

Temperature dependence of spin injection efficiency in an epitaxially grown Fe/GaAs hybrid structure

The electrical spin injection from Fe into an n-doped GaAs channel through Schottky-tunnel-barrier is observed from 1.8 K to room temperature. The magnitude of local spin valve signal (Δ R/ R 0) decreases as the temperature increases. In each temperature, we calculated the injected polarization ( η) considering the spin drift effect induced by the electric field. The interfacial polarizations of 19.3% and 12.6% are acquired for Fe/GaAs junction at T=1.8 and 300 K, respectively. The temperature dependence of spin injection efficiency is matched with interface resistance variation. As the temperature increases, Schottky-tunnel-barrier property is diminished so that the spin injection efficiency would be reduced.

Electrical Spin Transport in n-Doped In0.53Ga0.47As Channels

Spin injection from a ferromagnet into an n-doped <TEX>$In_{0.53}Ga_{0.47}As$</TEX> channel was electrically detected by a ferromagnetic detector. At T = 20 K, using non-local and local spin-valve measurements, a non-local signal of <TEX>$2\;{\mu}V$</TEX> and a local spin valve signal of 0.041% were observed when the bias current was 1 mA. The band calculation and Shubnikov-de Haas oscillation measurement in a bulk channel showed that the gate controlled spin-orbit interaction was not large enough to control the spin precession but it could be a worthy candidate for a logic device using spin accumulation and diffusion.