Vacancy-Induced Temperature-Dependent Thermal and Magnetic Properties of Holmium-Substituted Bismuth Ferrite Nanoparticle Compacts

Multiferroics have gained widespread acceptance for room-temperature applications such as in spintronics, ferroelectric random access memory, and transistors because of their intrinsic magnetic and ferroelectric coupling. However, a comprehensive study, establishing a correlation between the magnetic and thermal transport properties of multiferroics, is still missing from the literature. To fill the void, this work reports the temperature-dependent thermal and magnetic properties of holmium-substituted bismuth ferrite (BiFeO3) and their dependencies on oxygen vacancies and structural modifications. Two distinct magnetic transitions on temperature-dependent magnetic and heat capacity responses are identified. Experimental analysis suggests that the excess of oxygen vacancies shifts the magnetic transition temperature by ∼64 K. The holmium substitution-induced structural modification increases BiFeO3 heat capacity by 30% up to the antiferromagnetic phase transition temperature. Furthermore, an unsaturated heat capacity even at temperatures as high as 850 K is observed and is ascribed to anharmonicity and partial densification of the nanoparticles used during heat capacity measurements. The room-temperature thermal conductivity of BiFeO3 is ∼0.33 ± 0.11 W m–1 K–1 and remains unchanged at high temperatures due to defect scattering from porosities.