Spark plasma sintering of cobalt ferrite nanopowders prepared by coprecipitation and hydrothermal synthesis

Cobalt ferrite exhibits a high coercivity at room temperature and a strong magnetic anisotropy compared to the other spinel ferrites and, consequently appears as an interesting material for permanent magnets and high-density recording. The magnetic properties depend also on the crystallite size. In order to keep the powder properties in a bulk material, dense nanostructured cobalt ferrite has to be sintered. A field activated sintering process like spark plasma sintering (SPS) may be promising for such challenge. The present paper deals with: (i) the preparation of cobalt ferrite by two methods: coprecipitation and hydrothermal synthesis in supercritical water; (ii) the SPS sintering of the cobalt ferrite nanopowder prepared by coprecipitation. The sintering of the as-processed powder and that obtained after a thermal treatment resulting in the spinel phase has been investigated. The influence of the starting powder and the sintering parameters such as the temperature, the duration of the SPS stage on the grain growth and the densification degree of bulk materials will be presented.