Cobalt content dependences of cationic distribution and local fields in CoxFe3−xO4—Hyperfine interaction studies.

Co content (x) dependences of cationic distribution and local fields at the tetrahedral A-site and octahedral B-site nuclei in Co ferrites, Co_xFe_3−xO₄ (x = 0–1.0), were investigated by means of hyperfine interaction techniques. A combined investigation by ⁵⁷Fe transmission and ⁵⁷Co emission Mössbauer spectroscopies revealed that about 6% of Co²⁺ ions occupy the A sites for the sample with Co contents of x = 0 and 1.0. This observation evidently suggests that the site selectivity of Co²⁺ ions is independent of x for samples prepared on the same heat treatment condition. For hyperfine interaction parameters, obvious x dependence was observed for the B-site Fe nuclei, reflecting variation of the atomic ratio of Fe³⁺/Fe²⁺ changing with x, whereas for the A-site Fe nuclei, the parameters hardly change along with x. Contrary to the x-independence for the A-site Fe nuclei, however, it was demonstrated by perturbed angular correlation spectroscopy with the nonmagnetic probe ¹¹¹Cd(←¹¹¹In) that the hyperfine field at the A site significantly changes along with x. These contradictory results on the A-site fields verify that the nonmagnetic probe can distinguish a subtle change in the local fields with higher sensitivity. [ABSTRACT FROM AUTHOR]