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Register a new userEnhancement of Spin Injection into Graphene by Water Dipping
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We immerse single layer graphene spin valves into purified water for a short duration (<1 min) and investigate the effect on spin transport. Following water immersion, we observe an enhancement in nonlocal magnetoresistance. Additionally, the enhancement of spin signal is correlated with an increase in junction resistance, which produces an increase in spin injection efficiency. This study provides a simple way to improve the signal magnitude and establishes the robustness of graphene spin valves to water exposure, which enables future studies involving chemical functionalization in aqueous solution.
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We derive a drift-diffusion equation for spin polarization in semiconductors by consistently taking into account electric-field effects and nondegenerate electron statistics. We identify a high-field diffusive regime which has no analogue in metals. In this regime there are two distinct spin diffusion lengths. Furthermore, spin injection from a ferromagnetic metal into a semiconductor is enhanced by several orders of magnitude and spins can be transported over distances much greater than the low-field spin diffusion length.
The bias dependence of spin injection in graphene lateral spin valves is systematically studied to determine the factors affecting the tunneling spin injection efficiency. Three types of junctions are investigated, including MgO and hexagonal boron nitride (hBN) tunnel barriers and direct contacts. A DC bias current applied to the injector electrode induces a strong nonlinear bias dependence of the nonlocal spin signal for both MgO and hBN tunnel barriers. Furthermore, this signal reverses its sign at a negative DC bias for both kinds of tunnel barriers. The analysis of the bias dependence for injector electrodes with a wide range of contact resistances suggests that the sign reversal correlates with bias voltage rather than current. We consider different mechanisms for nonlinear bias dependence and conclude that the energy-dependent spin-polarized electronic structure of the ferromagnetic electrodes, rather than the electrical field-induced spin drift effect or spin filtering effect of the tunnel barrier, is the most likely explanation of the experimental observations.
Whereas spintronics brings the spin degree of freedom to electronic devices, molecular/organic electronics adds the opportunity to play with the chemical versatility. Here we show how, as a contender to commonly used inorganic materials, organic/molecular based spintronics devices can exhibit very large magnetoresistance and lead to tailored spin polarizations. We report on giant tunnel magnetoresistance of up to 300% in a (La,Sr)MnO3/Alq3/Co nanometer size magnetic tunnel junction. Moreover, we propose a spin dependent transport model giving a new understanding of spin injection into organic materials/molecules. Our findings bring a new insight on how one could tune spin injection by molecular engineering and paves the way to chemical tailoring of the properties of spintronics devices.
We demonstrate spin polarized tunneling from Fe through a SiO2 tunnel barrier into a Si n-i-p heterostructure. Transport measurements indicate that single step tunneling is the dominant transport mechanism. The circular polarization, Pcirc, of the electroluminescence (EL) shows that the tunneling spin polarization reflects Fe majority spin. Pcirc tracks the Fe magnetization, confirming that the spin-polarized electrons radiatively recombining in the Si originate from the Fe. A rate equation analysis provides a lower bound of 30% for the electron spin polarization in the Si at 5 K.
Electrical spin injection from the Heusler alloy Co_2MnGe into a p-i-n Al_0.1Ga_0.9As/GaAs light emitting diode is demonstrated. A maximum steady-state spin polarization of approximately 13% at 2 K is measured in two types of heterostructures. The injected spin polarization at 2 K is calculated to be 27% based on a calibration of the spin detector using Hanle effect measurements. Although the dependence on electrical bias conditions is qualitatively similar to Fe-based spin injection devices of the same design, the spin polarization injected from Co_2MnGe decays more rapidly with increasing temperature.
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