The crystal structure and magnetic properties of aluminium-substituted cobalt-ferrite nanoparticles synthesised by the co-precipitation are reported in this study. The single phase nanoparticles are obtained. Magnetic
property Changes in these properties are clarified mainly by changes in parameters such as the crystalline constant, crystallite size and crystalline density. An increase of saturated magnetisation with annealing temperature is also observed. Results for the change in saturated magnetization at several elevated temperatures indicate that the available non-magnetic aluminium ions support redistribution of cation-trivalent Fe³⁺ during the annealing process at octahedral sites.