Dielectric and magnetic properties in Ta-substituted BiFeO₃ ceramics

The dielectric and magnetic properties were investigated in Ta-substituted BiFeO₃ polycrystalline ceramics synthesized by a solid-state reaction. The Ta substitution decreased the grain size by two orders of magnitude compared with that of unsubstituted ceramics and increased the electrical resistivity by 6 orders of magnitude. The high resistivity and low dielectric loss allowed the dielectric constant to be determined at room temperature. The magnetic hysteresis loops were observed in the Ta-substituted BiFeO₃, and the appearance of ferromagnetism was closely associated with the distortion of the oxygen octahedra by the Ta substitution. The coupling between the electric and magnetic dipoles was examined by determining the changes of the dielectric constant with the external magnetic field.