Magnetic, Structural, and Magnetoelectric Coupling Properties of Aliovalent Substituted Multiferroic BiFeO₃nanoparticles

Multiferroics (MF) are materials that show spontaneous magnetic and electric ordering in the same phase. The coexistence of different functionalities (ferroelectricity, ferro-elasticity and ferromagnetism) in a single phase makes MF a remarkable candidate for the next generation electronic applications. Nanoparticles of multiferroic Bi_1-xCaxFeO₃  (x between 0.0 and 0.4) have been synthesized and the kinetics of magnetoelectric (ME) coupling in Bismuth Ferrite (BiFeO₃) with the substitution of aliovalent calcium ion has been investigated. Substitution induced structural transition from rhombohedral to the orthorhombic system is observed. The crystallite size obtained for the samples is well below the spiral spin wave length (62 nm) of Bi_1-xCa_xFeO₃ system. Comparison of dielectric and XPS studies reveals oxygen vacancies can be reduced upon calcium substitution upto 20at%. The ME coupling studies reveals a systematic increase in ME coefficient can be achieved up to 20 at% of calcium substitution, which is close to the theoretical predictions reported in the literature. We found that calcium ion is a suitable substituent to improve the properties by structural modification and control of parasitic phases as well as interstitial defects formation. The resulting structural, dielectric, magnetic and magnetoelectric coupling properties have been explained in terms of chemical pressure originating from the substituent ion.