Study of hyperfine interactions in spinel cobalt ferrite CoFe2O4 doped with Hf, Lu, and Yb using Mössbauer spectroscopy and perturbed γ-γ angular correlation

We studied hyperfine interactions (HFI) in spinel cobalt ferrite (ferrospinel) CoFe2O4 doped with Lu, Yb, and Hf (1 wt. %) by Mössbauer spectroscopy (MS) on 57Fe nuclei. The interactions indicate the presence (CoFe2O4:Lu – 11 %, CoFe2O4:Yb – 23.4%) and the absence (CoFe2O4:Hf) of additional phases. The study revealed a significant change in the HFI parameters on 57Fe nuclei in the octahedral sites in ferrospinels doped with Hf, Lu, and Yb. However, the relative influence of the impurity on 57Fe nuclei in the tetrahedral sites was insignificant. The parameters of hyperfine fields on 172Yb nuclei in cobalt ferrite were obtained by the method of perturbed γ-γ angular correlations (PAC). The 172Yb ions were introduced into the sample using two methods: by adding 172Hf and 172Lu isotopes. A significant difference in the HFI parameters for these two cases was revealed. The local environment of 172Yb ions appears to be different in the two variants of isotope introduction into the sample (Hf or Lu). The difference in the HFI parameters persisted in the temperature range of 300 - 1000 K. It was determined that the different effects of Hf and Lu on the parameters (electric field gradient, magnetic field, and isomer shift) of the HFI in the sample are revealed by both MS and PAC methods, irrespective of the amount of the dopant. According to the MS data, Hf and Lu do not lead to significant changes in the HFI parameters in the tetrahedral sites (“Sextet 1”), but have a significantly different effect on the same parameters in the octahedral sites (“Sextet 2”). A similar pattern was observed using the PAC method: replacing Hf with Lu did not reveal any changes in the HFI parameters in one of the sites (the octahedral site), but indicated a significant change in the other site