Transition from giant linear positive to negative magnetoresistance as a result of the metal insulator transition in cobalt nanosheet decorated graphene with high coercivity

Integration of superior electronic property of graphene and magnetic property of transition metal (TM) to achieve promising materials with excellent electronic and magnetic properties is an interesting area of research. Intrinsically, charge transport in pristine graphene and magnetic property in nanophase TM are well studied subjects. However, these properties deviate drastically from their intrinsic counterpart due to strong interaction at the interface when TM nanostructures are grown on graphene surface. So far no serious effort has been given to look at this issue. Therefore, in the present work, graphene sheet is decorated by Co nanosheets of average lateral dimension of ~15 nm to explore the basic understanding of charge transport, magnetism and magnetoresistance in these integrated structures. Very interesting metal–insulator transition is observed. The charge transport is explained by electron–electron interaction in the insulating regime as arising due to quantum interference and electron scattering in the metallic regime. The materials also show a high coercivity and a transition from giant linear positive magnetoresistance to nonlinear negative magnetoresistance. High coercivity in the present sample arises due to charge transfer, surface pinning and strain created at the graphene/Co interface while positive and negative magnetoresistances are explained on the basis of electron–electron interaction and electron-spin scattering respectively.