Defect driven d0 ferromagnetism and colossal dielectric behavior in Bi(Zn0.5Ti0.5)O3–PbTiO3 ceramics

Abstract

We report room temperature ferromagnetism and colossal dielectric behavior in non-magnetic polycrystalline samples of x (BiZn0.5Ti0.5O3) – (1-x) (PbTiO3) with x = 0.25, 0.50. These samples are synthesized by mechanical alloying followed by heating the samples at elevated temperatures. Room temperature X-ray diffraction study reveals the formation of BZT-PT samples in perovskite phase and in the tetragonal system. The magnetic properties of these samples are studied by using SQUID. Intriguingly, exotic room temperature ferromagnetism has been observed in non-magnetic BZT-PT samples by vacuum annealing of the samples. In addition, a substantial high dielectric constant has also been observed in vacuum annealed samples. The unprecedented magnetic and dielectric behavior has been attributed to the formation of oxygen vacancies which is explained by further studying the magnetic and dielectric behavior in air annealed samples. Furthermore, the dielectric relaxation and frequency response of ac conductivity in BZT-PT samples found to follow universal dielectric relaxation and Johnscher's power law response, respectively. A detailed density functional calculations show that the exotic magnetism BZT-PT is mainly due to the partial occupancy of t2g and eg states of Ti ion by the delocalized electrons generated due to oxygen vacancy.