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

SiO 2 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 SiO 2 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 SiO 2 (Co–SiO 2) thin films through chemical sol-gel based-spin coating processes. The thus obtained Co–SiO 2 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 SiO 2 (m -SiO 2) 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–SiO 2 films, and a paramagnetic behavior was observed at 50 K and above. The temperature-dependent magnetization (M vs. T) measurements of the Co–SiO 2 films also showed an increase of magnetization below 50 K. It is anticipated that Co substitutes Si although presence of the CoO and/or Co 3 O 4 phases cannot be completely ruled out. These results support the idea that a ferromagnetic-like transition takes place in the Co-doped SiO 2 films below 50 K due to Co doping. At the same time, a reduction in the leakage current density was determined in Co–SiO 2 , while maintaining better charge transfer in 1.0 M KOH for ion conducting devices. A successful doping of Co element in the framework of mesoporous SiO 2 thin films was demonstrated. The magnetization measurements support the idea that a ferromagnetic-like transition takes place in the Co-doped SiO 2 films below 50 K, while the bare SiO 2 did not show any magnetic properties. At the same time the leakage current was reduced by Co-doping with a slight increase in the dielectric constant (ε) due to Co doping, while maintaining better electric conductivity. [Display omitted] • Co-doped mesoporous SiO 2 (Co–SiO 2) thin films on Si were successfully prepared. • S-type shape on M vs H curves appeared at 5 K supports a ferromagnetic transition. • A paramagnetic behavior was observed at 50 K and above in the M vs. T curves. • The M vs T measurement also showed an increase of magnetization below 50 K. • The leakage current density was reduced, while maintaining better charge transfer. [ABSTRACT FROM AUTHOR]