ELECRTONIC AND MAGNETIC STATES OF IRON IONS IN (Bi1-xSrx)FeO3-y MULTIFERROIC PEROVSKITES

The mixed perovskites (Bi1-xSrx)FeO3-y (x = 0.07, 0.14, 0.25 and 0.50) were studied by Fe-57 Mossbauer spectroscopy in the temperature range 87-700 K. The samples were prepared by conventional ceramic technology with 10% Fe-57 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 T-N(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 Mossbauer 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.