Spin absorption by in situ deposited nanoscale magnets on graphene spin valves

TL;DR

This study quantifies spin current absorption by nanoscale metallic islands on graphene spin valves, revealing material-dependent absorption efficiencies and implications for spin transfer torque applications.

Contribution

It introduces an in situ measurement method to quantify spin absorption by nanoscale magnets on graphene, enabling controlled thickness variation and separation of absorption effects from injection mechanisms.

Findings

Fe absorbs spin current as high as 10^8 A/m^2

Absorption limited by graphene/Fe interface resistance-area product

Cu shows smaller spin absorption due to longer spin diffusion length

Abstract

An in situ measurement of spin transport in a graphene nonlocal spin valve is used to quantify the spin current absorbed by a small (250 nm $\times$ 750 nm) metallic island. The experiment allows for successive depositions of either Fe or Cu without breaking vacuum, so that the thickness of the island is the only parameter that is varied. Furthermore, by measuring the effect of the island using separate contacts for injection and detection, we isolate the effect of spin absorption from any change in the spin injection and detection mechanisms. As inferred from the thickness dependence, the effective spin current $j_e = \frac{2e}{\hbar} j_s$ absorbed by Fe is as large as $10^8$ A/m$^2$. The maximum value of $j_e$ is limited by the resistance-area product of the graphene/Fe interface, which is as small as 3 $\Omega\mu$m$^2$. The spin current absorbed by the same thickness of Cu is smaller than for Fe, as expected given the longer spin diffusion length and larger spin resistance of Cu compared to Fe. These results allow for a quantitative assessment of the prospects for achieving spin transfer torque switching of a nanomagnet using a graphene-based nonlocal spin valve.