Rietveld refinement analysis and influence of individual phases on the magnetoelectrically coupled (1-x)BSZT+ xNCZGF multiferroic composites

Abstract

The magnetoelectric voltage coefficient at room-temperature is realized in various (1-x)BSZT+ xNCZGF composites by studying refined crystal structures, surface morphology, magnetic, electric and ferroeletric properties. The ferroelectric (BSZT) and ferrite (NCZGF) phases of the composites are prepared using standard solid-state reaction technique. Rietveld refinement confirmed that the BSZT phase forms perovskite structure with P4mm space group and NCZGF phase forms spinel structure with Fd3¯m space group. From FESEM surface morphology it was observed that the average grain diameter ranges 0.5–2.21 µm. EDX analysis confirms the formation of respective phases and composites. Initial permeability increases from 55 to 130 with increasing NCZGF content which is consistent with the value calculated theoretically using different models. The saturation magnetization also increases from 12 to 37 emu/g with increasing NCZGF content, consistent with the calculated value using law of approach to saturation technique. The dielectric constant of the composites is found to decrease with increasing NCZGF content which is in line with the Maxwell-Garnett, Bruggeman, Looyenga and Lichteneker theoretical approximations. Frequency dependence of the dielectric constant exhibits dispersion, which can be modeled using a modified Debye function that considers the probability of several ions contributing to the relaxation. The ac conductivity follows the Jonscher’s power law, and the conduction mechanism is attributed to the small polaron hopping. Complex impedance is evaluated using the Cole-Cole plot ensures the dominance of both grain and grain boundary resistances. The P-E hysteresis loops ensure the typical ferroelectric nature at room-temperature for x ≤ 0.2. The simultaneous M-H and P-E hysteresis loops confirm the magnetoelectric coupling between ferrite and ferroelectric phases. Furthermore, the maximum magnetoelectric voltage coefficient for 0.9BSZT+ 0.1NCZGF composite is found to be ~194 mV cm−1 Oe−1 that can be used in multifunctional devices.