Magnetism and magnetotransport properties of heterostructures composed of magnetic nanoparticles onto graphene stacks

Full text: We have developed heterostructures that combine magnetic properties of magnetic nanoparticles and graphene. We have produced these nanostructures by chemical methods, by decorating oxidized graphene with maghemite nanoparticles grafted with a silane (3-aminopropyltriethoxysilane, APTES), then we submitted that structure to reduction. We have obtained the desired system in an adaptation of the methods of Massart, for maghemite nanoparticles; and Hummers, for obtaining graphene layers. We checked the conformation of the heterostructure by Scanning Electron Microscope, X-ray Diffraction, Fourier Transformed Infrared Spectroscopy, and thermogravimetric analysis. By magnetic susceptibility and magnetization vs temperature measurements we have ascertained that the system keeps superparamagnetic character coming from iron oxide nanoparticles, seen as characteristics peaks in those graphs at low temperatures. We have prepared these systems with two different nanoparticle sizes, with mean diameters of 10 and 100 nm, to study its influence on the electrical transport properties. We have recorded a logarithmic decreasing of the electrical resistance when temperature is raised. These heterostructures have mixed behaviors, because of the interplay of the nanoparticles and the graphene. Differences between those behaviors are interpreted in the light of the variable range hopping model. We will show some particularities in the magnetoresistance measurements. (author)