Giant ac magnetoconductivity in rGO-Fe3O4 composites

Abstract

In this work we report detailed investigations of structural, ac transport and magnetotransport properties of composites of reduced graphene oxide (rGO) and magnetite nanoparticles measured in the frequency range 10 Hz–2 MHz and in static magnetic fields upto 500 mT. AC conductivity of composite samples was enhanced by a factor of ~3 over that of the pure rGO even though the conductivity of magnetite is five orders of magnitude lower than that of rGO. We attribute this to charge transfer effects between the magnetite nanoparticles and the rGO matrix. Evidence of this is also observed in detailed Raman analysis of all samples. Further, we find a giant magnetoconductivity in the ac transport behavior of the composite samples. The rGO sample showed a negative magnetoconductivity of ~−15% at room temperature, while all composite samples showed positive magnetoconductivity with weak frequency dependence between 10 Hz and 254 kHz. We report a room temperature ac magnetoconductivity of 57% (at f = 254 kHz) and 40% (at f = 10 Hz) in a magnetic field B = 500 mT for the sample with 40 wt% magnetite nanoparticles. This is much larger than that obtained in dc magnetotransport, where room temperature magnetoconductivities in similar composites are typically 10% or less in comparable magnetic fields.