Spin Absorption by in Situ Deposited Nanoscale Magnets on Graphene Spin Valves

An in situ measurement of spin transport in a graphene nonlocal spin valve is used to quantify the spin current absorbed by a small (250×750nm2) 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 je=(2e/)js absorbed by Fe is as large as 108A/m2. The maximum value of je is limited by the resistance-area product of the graphene/Fe interface, which is as small as 3Ωμm2. The spin current absorbed by the same thickness of Cu is smaller than that 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.