Suppression of contact-induced spin dephasing in graphene/MgO/Co spin-valve devices by successive oxygen treatments

TL;DR

This study demonstrates that successive oxygen treatments improve contact resistance and suppress contact-induced spin dephasing in graphene spin-valve devices, significantly enhancing spin lifetime and signal amplitude.

Contribution

It introduces a method of oxygen treatment to increase contact resistance and reduce spin dephasing, leading to improved spin transport in graphene devices.

Findings

Spin lifetime and signal amplitude increased by a factor of seven.

Contact resistance area product ($R_cA$) increased with oxygen treatments.

Appearance of a second charge neutrality point (CNP) with increased $R_cA$.

Abstract

By successive oxygen treatments of graphene non-local spin-valve devices we achieve a gradual increase of the contact resistance area products ($R_cA$) of Co/MgO spin injection and detection electrodes and a transition from linear to non-linear characteristics in the respective differential dV-dI-curves. With this manipulation of the contacts both spin lifetime and amplitude of the spin signal can significantly be increased by a factor of seven in the same device. This demonstrates that contact-induced spin dephasing is the bottleneck for spin transport in graphene devices with small $R_cA$ values. With increasing $R_cA$ values, we furthermore observe the appearance of a second charge neutrality point (CNP) in gate dependent resistance measurements. Simultaneously, we observe a decrease of the gate voltage separation between the two CNPs. The strong enhancement of the spin transport properties as well as the changes in charge transport are explained by a gradual suppression of a Co/graphene interaction by improving the oxide barrier during oxygen treatment.