Graphene functionalized with 3-mercatopropionic acid capped zinc peroxide nanoparticles: A potential ferromagnetic material at room-temperature

The literature reveals that ferromagnetism in zinc peroxide (ZnO₂) is due to the exchange interaction between localized electron spin moments resulting from oxygen vacancies at the surface of nanoparticles, while in graphene may be due to existence of various defects. However ZnO₂ show paramagnetic behaviour, whereas graphene exhibits very low magnetic intensity (0.0004 emu g^-1). To enhance magnetization, graphene was treated with 3-mercatopropionic acid followed by coating with polyvinylpyrrolidone (PVP) capped ZnO₂ nanoparticles. Interestingly coating of graphene over ZnO₂ does not enhance magnetization, whereas coating of 15-20% ZnO₂ nanoparticles over graphene enhances magnetization more than 30 times, which gradually decreases on increasing concentration of ZnO₂ nanoparticles. Such coated graphene shows highest saturation of magnetization at room temperature ever reported in graphene (130 memu g^-1). The Magnetic measurements studies of ZnO₂ nanoparticles coated graphene indicates excellent room temperature ferromagnetic behaviour, which has been further confirmed by Electron Paramagnetic Resonance and Magnetic Force Microscopy studies. A comparative study was also done with ZnO nanoparticles with graphene and only 60 memu g^-1 magnetization has been observed. It has been concluded that higher magnetization in graphene coated with ZnO₂ than ZnO is due to more oxygen vacancies in ZnO₂ nanoparticles.