The influence of cation distribution on the magnetic properties of mixed Co1-yNiyFe2O4 nanoferrites produced by the sol-gel method

Mixed nanoferrites have been increasingly used as functional materials due to their versatile magnetic properties, associated with high surface energies. This work studied a series of mixed (Co1-yNiy)Fe2O4 nanoferrites with y = 0, 0.25, 0.5, 0.75 and 1.0, which were aimed to finely tune their magnetic properties by using composition manipulation. The synthesis was conducted via a nitrate/citrate sol-gel method associated with low annealing temperature, which provided easy control of cation distribution in the nanostructure. XRD results confirmed the formation of a cubic spinel phase for all the samples. TEM and BET results further confirmed the nanoscale (11-16 nm) size of the obtained particles of the materials. Raman and Mossbauer techniques allowed for the determination of the spinel inversion degree of the samples by estimating the population of Fe3+ cations at octahedral (B) and tetrahedral (A) sites. Nickel ferrite is arranged in an inverse spinel framework with soft magnetic behavior (H(c=)83 Oe; M(s=)41.72 emu.g(-1)), while the cobalt ferrite sample (CoFe2O4) shows a hard magnetic behavior (H(c=)894 Oe; M(s=)51.13 emu.g(-1)) with a structure of a partially inverse spinel. The considerable magnetic hardening upon Co2+ substitution is explained considering the increase in anisotropy energy and the decrease in inversion degree, which generate a net growth in the magnetic moment. This study is a further step towards understanding the inversion mechanisms involved in the fine-tuning of ferrimagnetic compounds. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

Mixed nanoferrites with varied compositions were synthesized using a nitrate/citrate sol-gel method. The different samples exhibited unique magnetic behaviors, with nickel ferrite showing soft magnetic properties and cobalt ferrite showing hard magnetic properties. The magnetic hardening upon Co2+ substitution was attributed to an increase in anisotropy energy and a decrease in inversion degree.