Coexistence of spontaneous polarization and magnetization in substituted M-type hexaferrites BaFe$_{12-x}$Al$_{x}$O$_{19}$ ($x\leq1.2$) at room temperature

Precision studies of the crystal and magnetic structures of substituted M-type barium hexaferrites BaFe$_{12-x}$Al$_{x}$O$_{19}$ ($x\leq1.2$) in the temperature interval of $300$–$760$ K have been performed by the power neutron diffraction method. The electric polarization and magnetization, as well as the magnetoelectric effect, of these compounds in electric (up to $110$ kV/m) and magnetic (up to $14$ T) fields at room temperature have been examined. The conservation of the collinear ferrimagnetic structure with substitution has been established. Spontaneous polarization and magnetization, as well as a strong coupling between the dielectric and magnetic subsystems at room temperature, have been revealed. The precision structural studies make it possible to determine the reason and mechanism of the appearance of spontaneous polarization in substituted M-type barium hexaferrites BaFe$_{12-x}$Al$_{x}$O$_{19}$ ($x\leq1.2$) with the collinear ferrimagnetic structure.