Spin-Current to Charge-Current Conversion and Magnetoresistance in a Hybrid Structure of Graphene and Yttrium Iron Garnet

The use of graphene in spintronic devices depends, among other things, on its ability to convert a spin excitation into an electric charge signal, a phenomenon that requires a spin-orbit coupling (SOC). Here we report the observation of two effects that show the existence of SOC in large-area CVD grown single-layer graphene deposited on a single crystal film of the ferrimagnetic insulator yttrium iron garnet (YIG). The first is a magnetoresistance of graphene induced by the magnetic proximity effect with YIG. The second is the detection of a dc voltage along the graphene layer resulting from the conversion of the spin current generated by spin pumping from microwave driven ferromagnetic resonance into a charge current, which is attributed to the inverse Rashba-Edelstein effect.

Figure 1

(a) Illustration of the YIG/graphene structures and the electrodes used to measure the magnetoresistance and the dc voltage due to spin-current to charge-current conversion. At mm size scale, the graphene should be represented as a continuous layer. (b) Raman spectroscopy spectra of GGG/YIG, ${\mathrm{SiO}}_2/\text{graphene}$, and GGG/YIG/graphene. (c) EDX spectrum from an arbitrary region in the sample of GGG/YIG/graphene.

Figure 2

(a) Magnetoresistance versus field $H$ calculated from the $M$ vs $H$ data of YIG/SLG (shown in the inset), as a function of the field applied in plane, transverse to the long dimension. (b) Measured field derivative of the resistance of graphene on YIG with increasing and decreasing field. Inset shows the $I\text{−}V$ curve of the YIG/SLG structure demonstrating the formation of Ohmic contacts between the electrodes and the SLG.

Figure 3

Field scan FMR microwave absorption derivative spectra at a frequency 9.4 GHz of three samples of $6\mu \mathrm{m}$ thick YIG film capped as indicated, with lateral dimensions $1.5\times 3.0{\mathrm{mm}}^2$, with the magnetic field applied in the film plane, normal to the long dimension.

Figure 4

Field scan spin-pumping dc voltage measured with 9.4 GHz microwave driving with power 150 mW in $\mathrm{YIG}(6\mu \mathrm{m})/\mathrm{Pt}(4\mathrm{nm})$ and $\mathrm{YIG}(6\mu \mathrm{m})/\mathrm{SLG}$, with the magnetic field applied in the film plane at the angles indicated in the inset of (a). The inset in (b) shows the linear variation of the peak voltage with microwave power in YIG/SLG.