The role of reduced graphene oxide capping on defect induced ferromagnetism of ZnO nanorods

In this study, the effect of different numbers of layers of reduced graphene oxide (RGO) on the ferromagnetic behavior of zinc oxide-reduced graphene oxide (ZnO-RGO) hybrid architectures has been investigated. Scanning and transmission electron microscopy along with x-ray diffraction of these hybrids confirm that ZnO nanorods are wrapped with different numbers of layers of RGO in a controlled way and their hexagonal phase is unaffected by these layers. Raman and photoelectron spectroscopy of these hybrids reveals that RGO does not alter the nonpolar optical phonon E(2) (high) mode and chemical state of Zn(2+) in ZnO. Electron paramagnetic resonance (EPR) spectra show that RGO passivates singly charged oxygen vacancies (VOS⁺) in ZnO. It correlates the passivation efficiency of VOS⁺ to the number of RGO layers and this has been achieved up to 90% by ∼31 layers of RGO. Due to passivation of VOS⁺ in ZnO by RGO, the ferromagnetic behavior (saturation magnetization and divergence between zero field cooled and field cooled) in ZnO-RGO hybrids is suppressed as compared to ZnO. Combining the EPR and magnetic behavior, a direct link between the passivation of the singly charged oxygen vacancies present on the surface of ZnO nanorods and the number of RGO layers is established.