Chemical engineering of cationic distribution in spinel ferrite nanoparticles: the effect on the magnetic properties

A set of ∼9 nm CoFe₂O₄ nanoparticles substituted with Zn²⁺ and Ni²⁺ was prepared by thermal decomposition of metallic acetylacetonate precursors to correlate the effects of replacement of Co²⁺ with the resulting magnetic properties. Due to the distinct selectivity of these cations for the spinel ferrite crystal sites, we show that it is possible to tailor the magnetic anisotropy, saturation magnetization, and interparticle interactions of the nanoparticles during the synthesis stage. This approach unlocks new possibilities for enhancing the performance of spinel ferrite nanoparticles in specific applications. Particularly, our study shows that the replacement of Co²⁺ by 48% of Zn²⁺ ions led to an increase in saturation magnetization of approximately 40% from ∼103 A m² kg^-1 to ∼143 A m² kg^-1, whereas the addition of Ni²⁺ at a similar percentage led to an ∼30% decrease in saturation magnetization to 68-72 A m² kg^-1. The results of calculations based on the two-sublattice Néel model of magnetization match the experimental findings, demonstrating the model's effectiveness in the strategic design of spinel ferrite nanoparticles with targeted magnetic properties through doping/inversion degree engineering.