Structural and magnetic properties of graphene-based Fe2O3-decorated composites

We present studies of structural and magnetic properties of graphene + Fe2O3 composite samples with the magnetic oxide content changing from 0 to 50%. Our studies revealed that irrespective of the cleaning procedure the magnetic behavior of pure graphene samples changed from diamagnetic to paramagnetic for samples made with either acetone or ethanol, respectively. The paramagnetic samples contained a significant concentration of magnetic moments. For all our samples with Fe2O3 at T < 110 K we observed the superparamagnetic blocking. Moreover, due to the presence of Fe2O3 nanoparticles with diameter >10 nm we observed a transition at T ≈ 495 K and another at T > 600 K. The synthesis solvent changes modified the magnetic behavior of our samples resulting in higher effective magnetic moment for the ethanol related samples. The shape and the parameters characterizing the magnetic hysteresis loop change strongly with the change of preparation method and the amount of Fe2O3. Large exchange bias was observed for all our samples indicating the significance of antiferromagnetic surface spin-alignment of Fe2O3 nanoparticles. It is therefore possible to control the magnetic properties of graphene + Fe2O3 composites over a wide range of parameters.