Phase Transition and Magnetoelectric Properties of BiFeO3-RMnO3 (R: Y3+, Gd3+, Dy3+) and Bi1-xBaxFe1-xZrxO3 Multiferroic Nanoceramics

Magnetoelectric multiferroics have triggered the attention of scientific community because of their intriguing fundamental physics and novel multifunctional device applications. BiFeO3 has been established as a prototype multiferroic materials having perovskite structure. However, the potentials of this material are yet to be realized due to several difficulties in synthesis, characterization and attaining the desired value of magnetoelectric coupling. The physical properties and the phase transition of this material vary as a function of intensive parameters (i.e., temperature, frequency, pressure, electric field and magnetic field). In the present dissertation, we have fabricated nanoceramic solid solution of (1-x)BiFeO3-xRMnO3 (R: Y3+, Gd3+, Dy3+) and Bi1-xBaxFe1-xZrxO3 with an aim to demonstrate enhanced magnetoelectric multiferroic properties. These modifications have induced a compositional driven structural phase transition and morphotropic phase boundary in the solid solution. The field emission scanning electron micrographs shows polycrystalline nature of microstructure. Temperature dependent dielectric study of BiFeO3 shows anomaly near antiferromagnetic transition temperature, 364 °C suggesting the signature of mgnetoelectric coupling in the material. The antiferromagnetic ordering temperature decreases towards room temperature with increase in composition. Improved ferroelectric hysteresis loops at room temperature have been observed. The grain and grain boundary contributions from the overall electrical properties have been separated using complex impedance spectroscopic analysis. The temperature variation of the bulk and grain boundary electrical conductivity obeyed the Arrhenius behavior suggesting the thermally activated conduction mechanism. The magnetization versus magnetic field curve for YMnO3 modified BiFeO3 samples has exhibited a switching behavior at low fields. Enhanced magnetization properties have been observed in GdMnO3 and DyMnO3 modified BiFeO3. A cross-over from antiferromagnetism to weak ferromagnetism is observed at x = 0.1 for Ba-Zr co-substituted BiFeO3with enhanced magnetization. The behavior of the magnetic hysteresis loops observed at room temperature suggests the suppression of space modulated spin structure. At room temperature, the dielectric permittivity of all the samples decreases with increasing magnetic field. The enhanced magnetoelectric coupling coefficient (ε(H)-ε(0))/ε(0) are found to be -5.5% (x = 0.2), -8% (x = 0.15) and -18% (x = 0.2) for YMnO3, GdMnO3 and DyMnO3 modification respectively at 2 Tesla. The temperature dependent dielectric properties, frequency dependent magneto-capacitance and magneto-impedance measurements demonstrate the signature of magnetoelectric coupling in the materials