Curvature-enhanced Spin-orbit Coupling and Spinterface Effect in Fullerene-based Spin Valves.

Shiheng Liang,Tho Duc Nguyen,Rugang Geng,Wenbo Zhao,Xiufeng Han,Baishun Yang,Xiaoguang Li,Ram Chandra Subedi

doi:10.1038/srep19461

Abstract

We investigated curvature-enhanced spin-orbit coupling (SOC) and spinterface effect in carbon-based organic spin valves (OSVs) using buckyball C60 and C70 molecules. Since the naturally abundant 12C has spinless nuclear, the materials have negligible hyperfine interaction (HFI) and the same intrinsic SOC, but different curvature SOC due to their distinct curvatures. We fitted the thickness dependence of magnetoresistance (MR) in OSVs at various temperatures using the modified Jullière equation. We found that the spin diffusion length in the C70 film is above 120 nm, clearly longer than that in C60 film at all temperatures. The effective SOC ratio of the C70 film to the C60 film was estimated to be about 0.8. This was confirmed by the magneto-electroluminescence (MEL) measurement in fullerene-based light emitting diodes (LED). Next, the effective spin polarization in C70-based OSVs is smaller than that in C60-based OSVs implying that they have different spinterface effect. First principle calculation study shows that the spin polarization of the dz2 orbital electrons of Co atoms contacted with C60 is larger causing better effective spin polarization at the interface.

Highlights

There exist several challenges on understanding spin loss mechanism and temperature dependence of spin diffusion length in OSECs18
There is very little effort to understand the effect of intrinsic spin-orbit coupling (SOC) in conventional OSEC-based spin valves
Various C60-based organic spin valves (OSVs) studies surprisingly show that the spin diffusion length in C60 varies from 10 nm to more than 100 nm, not significantly larger than in conventional OSECs29,30,33

Summary

Introduction

There exist several challenges on understanding spin loss mechanism and temperature dependence of spin diffusion length in OSECs18. Various C60-based OSVs studies surprisingly show that the spin diffusion length in C60 varies from 10 nm to more than 100 nm, not significantly larger than in conventional OSECs29,30,33. It is still not clear whether there exist any other spin loss mechanisms other than intrinsic SOC in fullerene. C60 and C70 fullerenes with quite distinctive topological phases (see Fig. 1c,d) may be the most sufficient choice for comparing the effect of curvature SOC on spin transport Such critical study has not been empirically achieved yet in fullerene-based spin valves. The latter is verified by the density functional theory (DFT) calculation

Methods

Results

Conclusion