Structure and Magnetic Properties of Co-Ni Spinel Ferrite Particles Synthesized via Co-Precipitation and Hydrothermal Treatment at Different Temperatures

Co-Ni spinel ferrite particles were synthesized via chemical co-precipitation and subsequently performed hydrothermal treatment at different temperatures. Fine particles of size with a few nanometers and spherical or cubic particles of size approximately 30 nm, which are responsible for magnetic properties, were obtained. The crystallite size obtained using the Scherrer equation was 24-27 nm and showed no dependency on the hydrothermal treatment temperature unlike the apparent particle size observed using transmission electron microscopy. The coercive force showed a remarkable increase with the decrease in the hydrothermal treatment temperature from 141 kA/m at 240℃ to 400 kA/m at 100-120℃, in contrast to the decrease in magnetization from 60.0 Am2/kg at 240℃ to 37.2 Am2/kg at 100℃. The specific composition of the Co-Ni spinel ferrite particles is expected to affect the high coercive force and the remarkable dependency of the coercive force on the hydrothermal treatment temperature.