Cationic exchange in nanosized ZnFe2O4 spinel revealed by experimental and simulated near-edge absorption structure

The nonequilibrium cation site occupancy in nanosized zinc ferrites (similar to 6-13 nm) with different degree of inversion (similar to 0.2 to 0.4) was investigated using Fe and Zn K-edge x-ray absorption near edge spectroscopy (XANES) and extended x-ray absorption fine structure, and magnetic measurements. The very good agreement between experimental and ab initio calculations on the Zn K-edge XANES region clearly shows the large Zn2+(A)-> Zn2+[B] transference that takes place in addition to the well-identified Fe3+[B]-> Fe3+(A) one, without altering the long-range structural order. XANES spectra features as a function of the spinel inversion were shown to depend on the configuration of the ligand shells surrounding the absorbing atom. This XANES approach provides a direct way to sense cationic inversion in these Zn-containing spinel ferrites. We also demonstrated that a mechanical crystallization takes place on nanocrystalline spinel that causes an increase of both grain and magnetic sizes and, simultaneously, generates a significant augment of the inversion.