Studies of phase transitions in Fe containing ternary perovskite multiferroics

One of the promising ways of designing new single-phase multiferroic materials is adjusting the temperatures of both ferroelectric and magnetic phase transitions by ion substitutions in the host compound to obtain the maximal magnetoelectric coupling. The aim of the present talk is a brief review of the recent studies of both ferroelectric and magnetic phase transitions in some Fe containing ternary perovskite multiferroics, especially PbFe_0.5B_0.5O₃ (B-Nb, Ta, Sb) and related solid solutions. Possible ways to control the temperature T_N of their antiferromagnetic phase transition are discussed. In our studies, besides the usual methods, we used the temperature evolution of ⁵⁷Fe Mössbauer spectrum as a sensitive method of T_N detection.

It is believed that in all perovskite ABO₃ multiferroics, magnetic and ferroelectric subsystems are independent. Magnetic properties are provided by B-site (e.g. Mn³⁺ and Fe³⁺) cations while ferroelectric properties are provided by the A-site cations having the so-called dangling bonds (Bi³⁺ and Pb²⁺). In contrast to this assumption, also A-site ion substitutions have been found to effect greatly the T_N value of PbFe_0.5B_0.5O₃. The results obtained are discussed using the models of magnetic superexchange involving Pb²⁺ cations and next-nearest Fe³⁺ neighbours.