Nanostructure of granularCo−SiO2thin films modified by thermal treatment and its relationship with the giant Hall effect

Abstract

Granular cosputtered ${\mathrm{Co}}_{52}{(\mathrm{Si}{\mathrm{O}}_{2})}_{48}$ thin films were thermally treated at different temperatures and their magnetotransport and structural properties were investigated. Hall resistivity increases with annealing temperature $({T}_{a})$, up to ${T}_{a}=250\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, and then decreases to a minimum for ${T}_{a}=400\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. The structural analysis was based on small-angle x-ray scattering results. A model of a polydisperse system of hard spheres was used to retrieve structural parameters. Results reveal that a volume fraction of Co atoms (approximately 25%) are forming nanospheres. The giant Hall effect depends on a particular combination of nanoparticle diameter, size distribution, and interparticle distance.