Controllable Magnetism of CoO Nanoparticles Modified by the Reduced Graphene Oxide

Rocksalt CoO nanoparticles (CNPs) have been prepared with a facile solvothermal method. To control the magnetism of CNPs, the reduced graphene oxide (RGO) is adopted to engineer the CNPs. Enwrapped by the atomic-layered carbon sheets, the CNPs can be reduced locally. The CoO/RGO composites were prepared by one-pot and two-pot synthetic methods, respectively. Compared with the CoO/RGO raw composite that have no magnetization hysteresis loop, the weak and the strong hysteresis loops emerged successively via heating the particles at different temperatures and maintaining their nanoscales. The magnetism can be adjusted by controlling the temperature via two routes. By the one-pot synthetic route, the CNPs can be reduced sharply, and an obvious hysteresis is available around 400 °C, which is ascribed to the appearance of Co nanoclusters decorated in the corners of CNPs. By the two-pot synthetic route, a weak and gradually enhanced hysteresis can be observed, and its magnetic properties should be ascribed to the topological defects of RGO. Our findings have opened a new way to acquire nanoparticles with controllable magnetism.