Evolution of morphology, structure and magnetic behavior of CdxZn1-xFe2O4@SiO2 nanocomposites with Cd2+ content and heat treatment

The influence of Cd²⁺ content and heat treatment on the morphology, structure and magnetic behavior of Cd_xZn_1-xFe₂O₄ (x = 0.0; 0.2; 0.4; 0.6; 0.8; 1.0) nanoparticles encapsulated in SiO₂ produced by the sol-gel route was studied. At 800 °C, Fe₂SiO₄, Fe₂O₃ and CdO accompanied the poorly crystallized ferrites, while at 1200 °C the well crystallized ferrite was convoyed by Zn₂SiO₄ and SiO₂. Encapsulation of nano-sized Cd_xZn_1-xFe₂O₄ in inert SiO₂ allowed the particle size control, minimized agglomeration, and improved the magnetic behavior. The low heat treatment temperature produced well-individualized nanoparticles of ∼40 nm, with the particle diameter being larger than the ferrite crystallites due to the SiO₂ coating. Increasing the Cd²⁺ content resulted in small particle size, whereas increasing the heat treatment temperature led to larger particle size, resulting in submicron clusters. The increase of Cd²⁺ content and heat treatment temperature also determined the increase in lattice constant, density and hopping length and the decrease in crystallite size and porosity. The nanoparticles were found to be mesoporous with a narrow pore size distribution. The magnetic features increased with heat treatment temperature and decreased with increasing Cd²⁺ content until paramagnetic-like behavior was reached for CdFe₂O₄.