Mössbauer Characterization of Electronic States and Local Surroundings of 57Fe and 119Sn in Ca-Substituted Lutetium Orthoferrites Lu1 – xCaxFe0.997Sn0.003O3

Abstract

The electronic state and local surrounding of both iron ions and tin dopant ions in Lu_{1 – x}Ca_xFe_0.997Sn_0.003O₃ (x = 0.003; 0.1; 0.2) compounds were studied by ⁵⁷Fe and ¹¹⁹Sn Mössbauer spectroscopy. The analysis of ⁵⁷Fe spectra showed that in the Lu_0.8Ca_0.2Fe_0.997Sn_0.003O₃ sample, obtained by air annealing, the charge deficit created by the substitution of Lu³⁺ by Ca²⁺ was compensated by the partial transition of Fe³⁺ to the +5 oxidation state. With a further increase in the value of x (in the Lu_0.8Ca_0.2Fe_0.997Sn_0.003O₃ compound) a mixed compensation mechanism appeared, including the formation of oxygen vacancies VO in addition to Fe⁵⁺ ions. Annealing the sample with x = 0.1 in H₂ at 400°C led to the reduction of Fe⁵⁺ to Fe³⁺ and, accordingly, to the pure vacancy mechanism of the Ca²⁺ charge deficit compensation. The analysis of ¹¹⁹Sn spectra showed that the substitution of Lu³⁺ by Са²⁺ in the Lu_0.8Ca_0.2Fe_0.997Sn_0.003O₃ structure led to the increase in the value of the magnetic field H, probed by some Sn⁴⁺ ions, as compared to the value of H> observed in the case of Lu_0.997Ca_0.003Fe_0.997Sn_0.003O₃. This change can be explained by a local increase in the angle of the indirect exchange interaction in the chain Fe³⁺–О₂––Sn⁴⁺, reflecting the presence of Ca²⁺ cation, larger than that of Lu³⁺, in the vicinity of Sn⁴⁺ ion.