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Synthesis and magnetic characterization of mixed CoFe2O4 spinel ferrite: Insights into structural properties, magnetic entropy, and tricritical behavior
Authors: Saidi, L.; Hajji, ABA; Hadded, S.; Benali, A.; Hlil, E.K.; Graça, MPF; Dhahri, E.; Costa, BFO
Ref.: J. Alloys Compd. 1048, 185083 (2025)
Abstract: In the present paper, the Cobalt spinel ferrite nanoparticles (CFO) were successfully synthesized throughout glycine Sol-gel self-ignition method. We validate the presence of a homogeneous cubic mixed-spinel ferrite phase identified by the Fd-3m space group according to a Rietveld analysis of the X-ray diffraction data, with the general formula (Co0.202Fe0.798)[Co0.789Fe1.202]O4. The synthesized CFO material presents an average crystallite size equal to 36.3 nm. Besides, optical measurements including UV-Vis absorption and photoluminescence revealed a broad emission band around 323 nm with an additional shoulder at 398 nm, attributed to the existence of multiple electronic transitions with a direct band gap of 1.95 eV. We additionally performed the analysis of the magnetic entropy, using the Maxwell formalism, while taking magnetic fields up to 3 Tesla into account. It´s maximum value (- Delta SM)max was found to be 1.42 J.Kg-1.K-1, leading to an RCP (relative cooling power) value of about 100 J.Kg-1. These interesting values allow the use of these nanoparticles in the magnetic refrigeration with low applied magnetic fields. Furthermore, we analyzed the critical parameters beta, gamma, and S using the Modified Arrott Plots (MAP) and the Kouvel-Fisher (KF) plots which were found to be respectively equal to 0.259, 1.029, and 4.887. These outcomes demonstrate how well the Tricritical-mean field model describes the long-range interactions in the CFO nanoparticles under investigation, which was confirmed as well from the exchange distance J(r) = r-4.624.
