Interplay between the cation distribution and production methods in cobalt ferrite

Microscopic, element selective structural and magnetic properties of cobalt ferrite produced by sol–gel (SG) and by ball milling (BM) methods were studied with X-ray absorption near-edge structure (XANES) spectroscopy and X-ray emission spectroscopy (XES). All investigated samples exhibit only Fe3+ and Co2+ cations. The relative distribution of the Co2+ and Fe3+ cations in the tetrahedral and octahedral sites depends on the production method of the samples. For the samples presenting a similar but small grain size (<400 nm), the quantity of Co2+ in B-sites of SG sample is less than that in BM sample. These results are in agreement with magnetic measurements, which BM samples exhibit smaller saturation magnetization as compared with those obtained for SG samples. Additionally the coercive field and magnetostriction are larger in BM samples. All these magnetic properties are dependent on annealing parameters (temperature and time). However for samples with large grain sizes their magnetic properties become insensitive to production processes.

► XANES spectra showed that distribution of Fe3+ and Co2+ ions over A- and B-sites depends on synthesis method.
► XES Co Kβ spectra showed that Co-spin state in SG samples varies with annealing temperature.
► Due to different cation distribution in A- and B-sites, these sample exhibit different values of Ms.
► For samples presenting a similar but small grain size, inversion degree is less in SG than BM samples.
► More Co2+ ions in B-sites results in higher anisotropy, which can result in larger Hc and λs.