New approach to closely-spaced disordered cobalt-graphene nanocomposites for non-conductive ferromagnetic films: From local structure to radio-electric properties

The objective of this work is to synthesize closely-spaced disordered nanocomposites of cobalt for producing μm-thick films of non-conductive ferromagnet with high moment . Commercial graphene-coated nanoparticles (Co/C) are used since graphene prevents metallic core from oxidation (i .e . saturation magnetization of 150emu/g). Synthesis of nanocomposites is based on two original functionalization schemes. First Co/C are functionalized by non-covalently grafting low molecular weight pyrene-terminated polystyrene (Pyr-PS₁) on graphene to obtain Co/C//PyrPS₁ product . Second Co/C//PS₁ is produced by covalent in situ polymerization of styrene monomers . As a result, uniform outer-shell successfully forms (2-4nm thick) around the nanoparticles of Co/C and avoids electric percolation while promoting strong dipolar coupling at room temperature . Thereby, we report that core double-shell particles of Co/C//Pyr-PS₁ or Co/C//PS₁ assembled in closely-spaced arrangements are strong enough to sustain different magnetic orders (antiferromagnetic, ferromagnetic, “amorphous-like”) both in cast solutions and films . At the end, a second high molecular weight polystyrene PS₂ is used as an encapsulating matrix to form Co/C//Pyr-PS₁/PS₂ or Co/C//PS₁/PS₂ final product suitable for spin coating .