The non-innocent role of cobalt in manipulating the magnetic and electric properties of mesoporous silica thin films

Abstract

SiO2 does not have magnetic elements; therefore, it behaves as a diamagnetic material with a possible paramagnetism due to oxygen vacancy defects. Incorporation of magnetic elements and pores into SiO2 films can add an additional functionality to its dielectric and insulating properties. Herein we report the incorporation of Co element into the mesoporous framework of SiO2 (Co–SiO2) thin films through chemical sol-gel based-spin coating processes. The thus obtained Co–SiO2 thin film exhibits transition in the magnetic properties, increase in the specific surface area and a decrease in the leakage current while maintaining better electric conductivity. For comparison, the bare mesoporous SiO2 (m-SiO2) films were prepared at identical conditions. Interestingly, a S-type shape on the isothermal magnetization measurements versus magnetic field (M vs. H) curves appeared at 5 K in case of the Co–SiO2 films, and a paramagnetic behavior was observed at 50 K and above. The temperature-dependent magnetization (M vs. T) measurements of the Co–SiO2 films also showed an increase of magnetization below 50 K. It is anticipated that Co substitutes Si although presence of the CoO and/or Co3O4 phases cannot be completely ruled out. These results support the idea that a ferromagnetic-like transition takes place in the Co-doped SiO2 films below 50 K due to Co doping. At the same time, a reduction in the leakage current density was determined in Co–SiO2, while maintaining better charge transfer in 1.0 M KOH for ion conducting devices.