The nonequilibrium cation site occupancy in nanosized zinc ferrites $(\sim 6–13\mathrm{nm})$ with different degree of inversion ($\sim 0.2$ 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 ${\mathrm{Zn}}^{2+}\left(\mathrm{A}\right)\to {\mathrm{Zn}}^{2+}\left[\mathrm{B}\right]$ transference that takes place in addition to the well-identified ${\mathrm{Fe}}^{3+}\left[\mathrm{B}\right]\to {\mathrm{Fe}}^{3+}\left(\mathrm{A}\right)$ 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.

• Received 13 September 2006

DOI:https://doi.org/10.1103/PhysRevB.75.073408