Magnetic properties and electric polarization at heterogeneous substitution in bismuth pyrostannate Bi2(Sn0,9Ме0,1)2O7, Ме= Cr3+, Fe3+

Bismuth pyrostannate Bi2Sn2O7 is a diamagnet and belongs to the structural type of the A2B2O7 pyrochlore class. In this class of compounds, in the presence of magnetic ions, very interesting magnetic properties appear. Chromium- and iron-substituted bismuth pyrostannates Bi2(Sn0.9Me0.1)2O7, Me = Cr, and Fe were synthesized by solid-phase synthesis. X-ray diffraction analysis showed that the samples correspond to the Pc monoclinic cell of the Bi2Sn2O7 α-phase at room temperature. The magnetic properties up to 1100 K in magnetic fields up to 0.86 T and the electric polarization at frequencies of 10, 3, and 1 mHz in the temperature range 80-550 K have been studied. The effect of heterogeneous substitution by Cr3+ and Fe3+ ions on the magnetic properties and electric polarization of bismuth pyrostannate is investigated. An analysis of the experimental data revealed the dependence of the magnetic properties on the degree of filling of the electron shells of chromium and iron ions. The Bi2(Sn0.9Cr0.1)2O7 compound exhibits ferromagnetic properties, while Bi2(Sn0.9Fe0.1)2O7 exhibits antiferromagnetic properties. In chromium-substituted bismuth pyrostannate during the α→β transition, the paramagnetic Curie temperature increases by a factor of 3. The temperature dependence of the inverse magnetic susceptibility is characterized by hysteresis in the temperature range of 400-900 K. The reverse magnetic susceptibility of Bi2(Sn0.9Fe0.1)2O7 in the entire temperature range is satisfactorily described by the Curie-Weiss law. Studies of the magnetic properties have established that the Fe3+ ions are in a high-spin state. The polarization hysteresis in Bi2(Sn0.9Cr0.1)2O7 is found, which shifts along the polarization axis and depends on temperature. Bi2(Sn1-xFex)2O7, x=0.1 is characterized by a linear field dependence. With an increase in the concentration of iron ions, a hysteresis arises in the field dependence of the electric polarization. The hysteresis of polarization in Bi2(Sn0.9Cr0.1)2O7 which depends on temperature was found. The nonlinear field dependence of the polarization in Bi2(Sn0.8Fe0.2)2O7 can be explained by the interaction of the dipole and migration polarizations and the presence of oxygen vacancies. For the Bi2(Sn0.9Cr0.1)2O7 compound, a transition to the dipole glass state was found. In the β-phase of Bi2(Sn0.8Fe0.2)2O7 above T = 400 K, no polarization hysteresis is observed and the electron-relaxation polarization predominates. The mechanism of the occurrence of electronic polarization is explained with the appearance of anionic vacancies upon heterogeneous substitution of tin ions.