Correlation between structure, morphology and magnetic properties in ZnxCo0.8-xNi0.2Fe2O4 @SiO2 (0.1÷0.7) nanocomposites

The structure, morphology and magnetic properties of ZnxCo0.8-xNi0.4Fe2O4 @SiO2 (x = 0.1; 0.3; 0.5; 0.7) nanocomposites (NCs) were investigated. The formation of the ferrites and SiO2 matrix was confirmed by X-ray diffraction that indicated the presence of low-crystalline single-phase Ni-Zn-Co spinel ferrite at 500 degrees C, well-crystallized Ni-Zn-Co spinel ferrite accompanied by Fe2SiO4 at 800 degrees C and by crystalline SiO2 (tridy-mite and cristobalite) at 1100 degrees C. In NCs with high Zn2+ content annealed at 1100 degrees C, traces of alpha-Fe2O3 were also noticed. The average crystallite size increased from 9.56 to 38.0 nm with the increase of annealing temperature and decreased with the increase of Zn2+ content. The scanning electron microscopy revealed large aggregates of irregular shapes. The transmission electron microscopy revealed the presence of both small and large spherical particles with a tendency to form agglomerates. The increase of Zn2+ content led to an increase of the number of low-size particles. The investigated NCs with high Co2+ content annealed at 1100 degrees C displayed ferrimagnetic behavior, while those with high Zn2+ content exhibited superparamagnetic behavior. The magnetic properties (saturation magnetization, remanent magnetization, coercivity and an-isotropy) evolved proportionally with the particle size and Co2+ content for the NCs annealed at 800 and 1100 degrees C, which is of high significance for possible applications in biomedicine as carriers for targeted drug delivery, hyperthermia treatment or magnetic resonance imaging agents.(c) 2022 Elsevier B.V. All rights reserved.