Cubic spinel ferrites are a class of oxides represented by the chemical formula AB2O4 with A and B being divalent and trivalent cations occupying octahedral and tetrahedral voids. Magnetization arises from superexchange interactions between cations via the oxygen anion. Among these, cobalt ferrites have been shown to undergo spinodal decomposition to form periodic microstructures at the nm length scale. The resultant changes in magnetic properties have been shown to be dependent on the periodicity and degree of decomposition. Complex nanostructured microstructures with concomitant spatial variations of intrinsic magnetic properties and magnetic interactions can yield wasp-waisted major hysteresis loops indicative of multiple magnetization reversal events1. Detailed analysis requires advanced magnetometry techniques, in order to disentangle reversible, irreversible, and viscous magnetization processes and their dependence on previous magnetic history. In this work, cobalt ferrite samples have been synthesized using standard powder processing techniques. Different degrees of decomposition have been achieved by varying the annealing time within the coherent spinodal range. TEM has been used to determine periodicity, degree of decomposition, lattice mismatch and the associated coherency strains between the decomposed phases. Magnetization processes occurring in these materials have been investigated through vibrating sample magnetometry using major M-H loops and temperaturedependent magnetization. These measurements have been complemented with non-saturating high-resolution first order reversal curve (FORC) diagrams obtained with different preconditioning fields, in order to explore magnetic states inaccessible to the major loops. Various switching events corresponding to the features observed in the FORC diagrams have been identified and correlated with microstructural observations. Finally, a better insight into the nature of the switching events has been obtained with Rayleigh loop measurements along selected FORCs.

References:

1. M. V. Suraj, A. Talaat, B. C. Dodrill, Y. Wang, J. K. Lee, and P. R. Ohodnicki Jr., AIP Advances 12, 035031 (2022)