Evolution of Structure and Magnetic Properties in EuxBi1-xFeO3 Multiferroics Obtained under High Pressure

Abstract

The structure, microstructure, magnetic properties and magnetocaloric effect in the BiFeO3-based multiferroics with a partial isovalent substitution of bismuth for europium ions have been experimentally and theoretically investigated by X-ray diffraction, SEM and magnetic methods. The ceramic EuxBi1−xFeO3 (0 ≤ x ≤ 0.2) samples have been prepared by a solid-state reaction method under cold pressing at high pressure P = 4 GPa. With increase in the concentration of the doping Eu element a structural phase transition from a rhombohedral R3c to an orthorhombic Pn21a perovskite structure is observed. Microstructure and chemical composition of the EuxBi1−xFeO3 samples have been studied by SEM data. Temperature dependences of magnetization for the Eu- doped multiferroics demonstrate two magnetic “weak ferromagnetic-antiferromagnetic” and “anti- ferromagnetic-paramagnetic” phase transitions in a high temperature range T = 640–822 K. The presence of a weak ferromagnetism in all compositions is confirmed by open loops of magnetic field dependencies. On the basis of the analysis of magnetic data, magnetic entropy change, heat capacity change, relative cooling power and full-width at half-maximum of the peak have been calculated. It has been found out that the thermodynamic characteristics strongly depend on the degree of substitution, temperature, and magnitude of magnetic field.