Scaling of the Nonlocal Spin and Baseline Resistances in Graphene Lateral Spin Valves

Abstract

Graphene lateral spin valves (LSVs) are promising devices for future memory and magnetic field sensing applications. In this article, we study the dependence of the nonlocal spin resistance, RNL, and the baseline resistance, RBS, as a function of the graphene channel width, W. The scaling trend is quantitatively assessed by using graphene deposited by chemical vapor deposition, which provides a large number of devices with consistent performance. As Wis scaled from 10 to 0.5 μm, the change in RNL matches the theory of contact-induced spin relaxation with a current spin polarization of 3%-5% and a spin diffusion length of λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> = 1.5-2.5 μm. We also observe a systematic and dramatic decrease in RBS, which we attribute to the reduction in charge current spreading. However, we find in the narrowest devices that a small RBS remains that arises due to thermoelectric effects, and this trend is confirmed using gate voltage and charge current-dependent analyses. Finally, we introduce a nonideality factor, m = |RBS/RNL|, as a figure of merit to describe the suppression of the baseline relative to the spin signal. In an LSV with L = 1.5 μm, W = 0.5 μm, and n-type conduction, the nonideality factor is as low as m = 0.0252 ± 0.0202 at room temperature showing that nearly ideal bipolar and symmetric spin signals can be achieved in graphene LSVs.