Piezoresponse and magnetic properties of multiferroic (1- x)Bi_0.9Dy_0.1FeO₃- x PbTiO₃ solid solution

The multiferroic solid solution of (1-x)[0.9BiFeO₃-0.1DyFeO₃]-xPbTiO₃ with compositions around the morphotropic phase boundary has been synthesized in the form of ceramics and characterized by Piezoresponse Force Microscope (PFM) and Superconducting Quantum Interference Device. Both the original local polar domain structure and the domain evolution after poling have been studied by PFM. The PFM phase imaging has revealed some interesting details of poling and domain switching process: The out-of-plane phase image shows a uniform direction of polarization along the applied electric field, while the in-plane phase image indicates two kinds of domains with antiparallel polarizations. This kind of poled domain structure is explained based on the orientations of the polarization as permitted by the rhombohedral crystal symmetry in grains of different crystallographic orientations. The magnetic properties measured within the temperature range from 1.8 K to 300 K reveal an interesting sequence of magnetic transitions from a weakly ferromagnetic order (WFM₁) to an antiferromagnetic state (AFM), and then to another weak ferromagnetic phase (WFM₂), upon cooling. A preliminary magnetic phase diagram is proposed for BDF-34PT.