Abstract:
Various multiferroic composites xLi0.1Mn0.6Ni0.2Fe2.1O4 + (1-x)Bi1-yRyFeO3, (where,
R = Y and Dy; x = 0.00, 0.10, 0.20, 0.30, 0.40, 0.50 and 1.00; y = 0.0 and 0.2) have been synthesized by the standard solid state reaction technique. The structural, complex initial permeability, dielectric properties, ac conductivity, impedance spectroscopy,
M-H hysteresis loop and magnetoelectric coefficient of the composites have been investigated thoroughly. The X-ray diffraction analysis has confirmed that the composites are composed of a mixture of ferrite and ferroelectric phases. The ferrite phase Li0.1Mn0.6Ni0.2Fe2.1O4 (LNMFO) forms cubic spinel structure. On the other hand, ferroelectric phases BiFeO3 (BFO) and Bi0.8Y0.2FeO3 (BYFO) show distorted rhombohedral crystal structure, but Bi0.8Dy0.2FeO3 (BDFO) shows the orthorhombic crystal structure. In the composites, there is a small change in the lattice parameters of both ferrite and ferroelectric phases, due to the stress exerted on each other. The bulk and X-ray density decrease linearly with ferrite content for all composites. The average grain diameter (D ̅) decreases for xLNMFO + (1-x)BFO composites, but for xLNMFO + (1-x)BDFO and xLNMFO + (1-x)BYFO composites, the D ̅ slightly decreases with ferrite part upto x = 0.1 and for further increase it has increased. Largest average grain diameter (9.03 μm) is observed for LNMFO. The real part of dielectric constant (ε^') for all composites exhibit usual dielectric dispersion due to Maxwell-Wagner type interfacial polarization. For all composites, the ε^' and dielectric loss (tanδ_E) decreases with ferrite content. The xLNMFO + (1-x)BDFO shows maximum ε^' (2845 at 10kHz) and minimum 〖tanδ〗_E (less than 1.5). The ac conductivity of composites follows the Jonscher’s power law and increases with frequency, indicating that the conduction is due to small polaron hopping. Impedance spectroscopy studies indicated presence of both the grain and grain boundary conduction mechanism. The real part of initial permeability has increased with ferrite content for all composites. However, xLNMFO + (1-x)BYFO composites show relatively higher initial permeability (43 for x = 0.5) compared to other composites. The xLNMFO + (1-x)BYFO composites show relatively higher M_s (22.74 Am2/kg for x = 0.5) compared to other xLNMFO + (1-x)BFO and xLNMFO + (1-x)BDFO composites. The magnetoelectric voltage coefficient for all composites decreases with ferrite content for x ≥ 0.1 and maximum value (182×103 Vm−1T−1) is found for 0.1LNMFO + 0.9BYFO composite.
