Cation concentration effects on structural, morphological, and magnetic behavior of CoMg₀.₅Fe₁.₅O₄ via reverse annealing

Abstract

Annealing-induced diffusion in nanoparticles reveals that variations in cation concentration at the tetrahedral A-site and octahedral B-site significantly influence the properties of ferrites. In this study, Co-ferrite nanoparticles doped with 0.5Mg at the octahedral B-site were synthesized via a wet chemical co-precipitation method and systematically annealed at 750 ◦C, 700 ◦C, 650 ◦C, and 600 ◦C. Rietveld refinement reveals that, as the annealing temperature decreases from 750 ◦C to 650 ◦C, the concentrations of Co²⁺, Mg²⁺, and Fe³ ⁺ in the octahedral B-site increase from 0.10 % to 0.90 %, 22.05–22.45 %, and 24.35–27.00 %, respectively, while Co²⁺ and Fe³ ⁺ concentrations in the tetrahedral A-site decrease from 99.90 % to 99.10 % and 53.60 % to 50.55 %, respectively. XRD analysis confirms the formation of a face-centered cubic (f.c.c.) spinel structure with an Fd-3‾m space group, accompanied by a reduction in crystallite size from 20.29 nm to 10.93 nm and an increase in dislocation density from 2.43 f-lines/m² to 8.37 f-lines/m². Additionally, the interionic bond lengths and bond distances decrease, while bond angles change in response to the variation in cation concentrations. FE-SEM images reveal well-defined nanostructures with relatively spherical grains, whose average sizes decrease from 20.69 nm to 11.20 nm with annealing. LCR bridge measurements show that the average complex permeability increases from 27.36 KHz to 35.31 KHz, while the magnetic loss factor decreases from 1.92 K to 1.49 K. Notably, the cation redistribution reflected in variations of cation concentration induced by reverse annealing leads to reduced crystallite and grain sizes, enhanced magnetic permeability, and decreased magnetic loss, effectively simulating compositional doping through cation concentration.