Composition control of magnetoelectric relaxor behavior in multiferroic BaZr0.4Ti0.6O3/CoFe2O4 composites

The (BaZr0.4Ti0.6O3)(1 - x)/(CoFe2O4)(x) (abbreviated as BZT(1 - x)/CFOx; x = 0.10, 0.15, 0.20 and 0.25) poly-crystalline composites are synthesized by a high-temperature solid state reaction technique. The effect of CFO composition on magnetoelectric-relaxor characteristics of the composites is thoroughly investigated. Detailed structural analysis of the composites by Rietveld refinement technique and first principles based density functional calculations reveal a macroscopic cubic structure with coexistence of Pm (3) over barm(for BZT), Fd (3) over barm(for CFO) space groups and a microscopic lower symmetry tetragonal structure with P4mm space group (indicating the presence of polar-nano-regions). To probe the relaxor behavior, the dielectric measurements were carried out in the wide frequency (1 kHz-1 MHz) and temperature (90-300 K) domain. It is observed that all the composite samples exhibit low temperature ferroelectric behavior. For some composite samples (0.10 <= x <= 0.20), the ferroelectricity is of relaxor-type. The relaxor behavior of the materials was further explained by Vogel-Fulcher type freezing of polar-nano-regions. The composite sample with x = 0.25, exhibits diffuse type ferroelectric phase transition with high value of diffusivity parameter (gamma = 1.98). Though BZT is paraelectric at room temperature, nevertheless the appearance of saturating P-E loops, gradual enhancement of remnant polarization with CFO ratio and co-occurrence of saturating M-H loops confirm the room temperature magnetoelectricity in composites. The impedance spectroscopic method is also employed to explain the influence of the conduction mechanism on ferroelectricity. The BZT/CFO composites with low temperature relaxor/diffuse phase ferroelectricity and room temperature magnetoelectricity can be exploited for both capacitor and memory device applications. (C) 2015 Elsevier B.V. All rights reserved.