Charge-induced artifacts in non-local spin transport measurements: How to prevent spurious voltage signals

Abstract: To conduct spin-sensitive transport measurements, a non-local device geometry is often used to avoid spurious voltages that are caused by the flow of charges. However, in the vast majority of reported non-local spin valve, Hanle spin precession, or spin Hall measurements background signals have been observed that are not related to spins. We discuss seven different types of these charge-induced signals and explain how these artifacts can result in erroneous or misleading conclusions when falsely attributed to spin transport. The charge-driven signals can be divided into two groups: Signals that are inherent to the device structure and/or the measurement setup and signals that depend on a common-mode voltage. We designed and built a voltage-controlled current source that significantly diminishes all spurious voltage signals of the latter group in both DC and AC measurements by creating a virtual ground within the non-local detection circuit. This is especially important for lock-in-based measurement techniques, where a common-mode voltage can create a phase-shifted, frequency-dependent signal with an amplitude several orders of magnitude larger than the actual spin signal. Measurements performed on graphene-based non-local spin valve devices demonstrate how all spurious voltage signals that are caused by a common-mode voltage can be completely suppressed by such a current source.