Phase Transitions and Magnetoelectric Coupling in Bi1-xAxFeO3 (A=La, Nd) Multiferroic Ceramics

The polycrystalline samples of Bi1-xAxFeO3 (A=La, Nd; x=0-0.2) were prepared by a conventional solid-state reaction method. The effects of varying the Nd and La doping concentration on the crystalline structures, magnetic properties and temperature of antiferromagnetic phase transition TN of the Bi1-xAxFeO3 compounds have been investigated. It is found that Nd doping resulted in a sequence of structural phase transitions and the destruction of the space modulated spin structure near x=0.15 in these materials.The temperature dependences of the magnetic ac-susceptibilities of the samples were obtained. The ac-susceptibility vs. temperature curve of BiFeO3 has a sharp peak at 646 K that corresponds to the antiferromagnetic phase transition TN. With the increase of rare-element doping concentration for both series of samples the Neel temperature TN shifts toward high temperatures.Specific heat capacity for all series of samples was measured in the temperature range of 350–750 K with the modulated-temperature differential scanning calorimeter. The phase transitions from antiferromagnetic to paramagnetic state were observed for all samples. The measurements of magnetocapacitance indicated the dependence of the magnetodielectric effect from the doping level of the rare-earth substitution x.