ИСТИНА

57Fe Mössbauer study of the SSMS as well as electric and magnetic hyperfine interactions in multiferroics BiFe1−xCrxO3 with rhombohedral structure were carried out. The Mossbauer spectra have been analyzed in terms of the incommensurate anharmonic SSMS of cycloid type model. The synthesis of the samples with x = 0.05, 0.10, 0.20 was performed under a pressure of 6 GPa at a temperature of 1250 K for 1.5 h. Phase composition of samples was characterized by X-ray diffraction. All substituted ferrites contained the positions of the iron atoms in the first cation coordination sphere of which there are one, two, three, and four atoms of Cr depending on the composition of ferrites. The temperature ranges of existence of incommensurate anharmonic SSMS of the cycloid type were determined for these ferrites. The parameter of anharmonicity m increases with increasing concentration of chromium in ferrites. Based on the data obtained, a magnetic phase diagram was constructed (see figure). Figure. Magnetic phase diagram of the system of Bi1-xCrxFeO3 in the axes of "the impurity concentration xCr" – "temperature T": PM – region of the paramagnetic state, SSMS (axis) – area anharmonic SSMS (axis) with magnetic anisotropy of "easy axis", SSMS (plane) – anharmonic SSMS with magnetic anisotropy of "easy plane", the AFM – region of antiferromagnetic ordering. In the framework of the model of SSMS, the temperature dependences of the hyperfine parameters of the 57Fe Möossbauer spectrum – the isomer shift, the quadrupole shift of the spectral components, isotropic and anisotropic contributions to the hyperfine magnetic field – were obtained and analyzed.