In-depth structural characterization and magnetic properties of quaternary ferrite systems Co0.5Zn0.25M0.25Fe2O4 (M = Ni, Cu, Mn, Mg)

This paper investigates the structural and magnetic properties of a mixed series of ferrites having general formula Co0.5Zn0.25M0.25Fe2O4 (M Ni, Cu, Mn, Mg). Insights on surface chemistry, structural and morphological parameters are presented in order to achieve highly tuned ferrite systems with specific characteristics. The site occupancy of the cations in the spinel structure was determined using XAS, XRD and Raman spectroscopy. A 100% occupancy of the tetrahedral sites was observed for the Zn cations for all the samples. Co cations occupied the octahedral sites in proportion of 100% for Co-Zn-Cu, Co-Zn -Mg and around 80% for Co-Zn-Ni, Co-Zn-Mn. Ni cations were found only in the octahedral sites, while Cu 80% in the octahedral sites and Mn 60% in the octahedral sites. The cation distribution results were correlated with the magnetic properties data. At the same time, not only the cation distribution, but also the particles size distribution was observed to have a great influence on magnetic and optical properties of the ferrites. Given the importance of the surface chemistry of the nanoparticles, XPS and FTIR analysis were used to prove the functionalization with groups belonging to the surfactant. Moreover, the peculiar behavior of manganese in spinel structures was clarified and the origin of the multiple states (Mn(2+)and Mn4+) was elucidated. Finally, parallels have been drawn between the use of different cations in mixed ferrites in order to gain specific properties. (C) 2019 Elsevier B.V. All rights reserved.