Papers by Author: V. S. Pokatilov

Abstract: Structure, valence and magnetic states of iron ions of the nanodispersed magnetite stabilised by a dielectric matrix have been studied by the ⁵⁷Fe Mössbauer spectroscopy, X - ray and electronic microscopy.

Abstract: 57Fe Mössbauer study of the Bi1-xLaxFeO3 (х=0, 0.1, 0.2, 0.61, 0.9, 1.0) perovskites has been performed at room temperature (RT) to analyze influence of the space spin-modulated magnetic structure (SSMMS) on parameters of hyperfine interactions, the valence and magnetic states of iron ions. SSMMS in perovskites BiFeO3 and Bi0.9La0.1FeO3 leads to a specific distribution of hyperfine fields P(H) with two peaks. Substitution La for Bi more than х = 0.2 destroys SSMMS and P(H) corresponds to a distribution for a homogeneous spin structure. Concentration dependences of hyperfine fields (H), isomer (δ) and quadrupole (ε) shifts were measured. Due to the isomer shift values the iron ions are in the trivalent state. The local magnetic moments μ(Fe) on Fe+3 ions were determined in these perovskites.

Abstract: The mixed perovskites (Bi1-xSrx)FeO3-y (x = 0.07, 0.14, 0.25 and 0.50) were studied by 57Fe Mössbauer spectroscopy in the temperature range 87–700 K. The samples were prepared by conventional ceramic technology with 10% 57Fe isotope enrichment. X–ray diffraction measurements showed that the samples were single-phase and had a rhombohedral structure at x = 0.07 and a cubic one at x = 0.14-0.50. As the strontium content x increases, the Neel temperature TN(x) increases from 640 K (x = 0) to 670 K (x = 0.25) and then decreases to 637 K (x = 0.5). The similar dependence on x was found for the hyperfine field values B(x) at T = 87 K. The experimental Mössbauer spectra are satisfactorily described by three to four Fe3+ states with the room temperature isomer shift values in the range 0.17-0.43 mm/s, which correspond to the iron sites with 4, 5 and 6 oxygen neighbours.