Large Low-Magnetic-Field Magnetocapacitance Effect and Spin Accumulation in Graphene Oxide

We report large magnetocapacitance (MC) effect and spin accumulation in graphene oxide (GO) studied at low magnetic fields and low frequencies, synthesized using modified Hummer’s method. Raman spectroscopy, atomic force microscopy (AFM), vibrating sample magnetometry (VSM), impedance spectroscopy, and dc transport measurements are used to investigate the origin of spin accumulation in GO. It was observed that synthesized GO was flake-like in morphology with prominent
$G$
- and
$D$
-bands of vibrations, with large defect density. It was found to have ferromagnetism with coercivity of the order of
$\sim 134$
Oe. The GO showed MC of 20% at around 200 Hz and 100 Oe, where capacitive coupling is higher and 2.2% at 1.1 MHz where inductive coupling is higher in the capacitor under study. The relaxation process in GO was modeled using modified Havriliak–Negami (H–N) approach for inhomogeneous medium, which predicted the spin accumulation length of the order of
$187~\mu \text{m}$
. The spin accumulation in GO here is proposed to be due to weak localization and exchange interaction at lower fields below coercivity and above it is interface mediated and dipolar in nature. The results are supported with dc–magnetoresistance (MR) study showing the depletive nature of the defects dominating the magnetic scattering process. The observations in GO are compared with reduced GO (rGO) which did not show significant spin accumulation. The comparison of data yields a proof of defect-mediated MC in GO.