Effect of particle size on multiferroism of barium-doped bismuth ferrite nanoparticles

Barium-doped bismuth ferrite (Bi1−xBaxFeO3 (x=0 and 0.15)) nanoparticles synthesized by a sol–gel method have been found to exhibit strong influence of size on structural, morphological, magnetic and dielectric properties. The size of Ba-doped BiFeO3 nanoparticle has been tailored via variation of calcination temperature. Structural analysis reveals the stabilization of rhombohedral phase for x=0.15 Ba-substitution in BiFeO3 lattice. Undoped BiFeO3 nanoparticles have been found to possess saturation magnetization value of 2.535 emu/g. Ba-substitution, enhancing ferromagnetism by about 1.7 times, is ascribed to suppression of spin cycloidal by oxygen vacancies created due to divalent substitution at trivalent site. Further, this value decreases as the particle size of doped nanoparticles increases owing to the decreasing surface to volume ratio. The magnetic phase transition temperature value registers a decay of 0.86 times with Ba-doping in comparison to undoped BiFeO3 nanoparticles. Also, the doped nanoparticles exhibit strong particle size dependence. Decreasing magnetic exchange interactions with reducing particle size leads to lowering of Nèel temperature. Ba-substitution has been found to result in decay of dielectric properties by about 0.85 times due to creation of oxygen vacancies. This property further decreases with increasing particle size of doped nanoparticles. These observations reveal strong correlation of size and multiferroism.