Spatial Spin-Modulated Structure of Bi1 – xSrxFeO3 – y (x = 0, 0.05, and 0.10) Multiferroics

The room-temperature X-ray and Mössbauer data on the BiFeO₃, Bi_0.95Sr_0.05FeO_{3 – y}, and Bi_0.90Sr_0.10FeO_{3 – y} multiferroics obtained by solid-phase synthesis are presented. The samples have a rhombohedral crystal structure with the sp. gr. R3c. The lattice parameter a_h is invariable, while the parameter c_h decreases with increasing strontium content. The ⁵⁷Fe Mössbauer spectra recorded at a temperature of 295 K have been interpreted within the cycloid spatial spin-modulated structure model. It has been established that the easy-axis magnetic anisotropy is implemented in the investigated multiferroics. The anharmonicity parameter m of the spin-modulated structure has been measured. Upon replacement of trivalent Bi³⁺ ions in small amounts (x = 0–0.10) with divalent Sr²⁺ ions, the parameter m increases by a factor of more than 3: from 0.10(4) at x = 0.00 to 0.36(10) at x = 0.10.