Enhancement of ferromagnetism and ferroelectricity by oxygen vacancies in mullite Bi2Fe4O9 in the Bi2(Sn0.7Fe0.3)2O7-x matrix

https://doi.org/10.1016/j.jmmm.2022.169530

A new bismuth pyrostannate-based composite Bi2(Sn0.7Fe0.3)2O7-x/Bi2Fe4O9 (BSFO/BFO) has been obtained by the solid-state synthesis. Temperature dependences of the magnetic hysteresis and remanent magnetization and the nonlinear field dependence of the magnetization for the Bi2Fe4O9 antiferromagnet have been established. A temperature of the formation of canted sublattices in the antiferromagnet with the occurrence of a spontaneous moment in mullite has been determined. The mechanism of the electric polarization hysteresis and the temperature dependence of the remanent polarization have been established. It has been shown, that, below the Néel temperature, the dipole polarization is induced by a lone electron pair of bismuth ions. At T > TN, the migration polarization is caused by the charge carrier density at the chemical potential. A significant increase in the remanent magnetization of mullite in the bismuth pyrostannate matrix with oxygen vacancies over a value typical of polycrystalline mullite has been established. Remanent magnetization is explained in terms of ferron model.