High coercivity in SiO2-doped CoFe2O4 powders and thin films

Mössbauer and magnetic studies have shown that 1–2 wt % of ${\mathrm{SiO}}_2$ could be dissolved in the ${\mathrm{CoFe}}_{\mathrm{2}}{\mathrm{O}}_4$ structure. Changes in magnetization and Curie temperature were observed. The presence of ${\mathrm{SiO}}_2$ might enhance magnetic anisotropy. Coercivity values of up to 3.5 kOe were measured for mechanically alloyed ${\mathrm{CoFe}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{4}}{\mathrm{/SiO}}_2$ powders. High coercivities were also achieved in ${\mathrm{SiO}}_2$ -doped Co–ferrite thin films prepared by sputtering technique. The Co–ferrite thin film deposited on a silicon wafer using a 5 wt % ${\mathrm{SiO}}_{\mathrm{2}}\mathrm{/Co}$ –ferrite target possessed a coercivity of 7.4 kOe. Spring-magnet behavior was observed, indicating the possible presence of remanence enhancement due to exchange coupling because of nanocrystalline structure.