Abstract

Magnetoelectric (ME) coupling in multiferroic materials plays an important role in designing multifunctional devices because of their potential to tune polarization via a magnetic field or magnetism via an electric field. However, the single-phase ME materials have not been successfully explored in practical devices due to their low ME coupling coefficient. Here, we optimized the magnetic and magnetoelectric response of single-phase Bi1− xYxFe0.7Mn0.3O3 compounds by controlling the Y substitution and sintering temperature. Single-phase Bi1− xYxFe0.7Mn0.3O3 (where x varies from 0 to 0.20 in the step of 0.05) compounds were prepared by a standard solid-state reaction technique. The optimum sintering temperature and yttrium substitution were found to be 825 ◦C and x = 0.10, respectively, in which the sample shows the optimum microstructural, magnetic, and ME properties at room temperature. The optimized Bi0.9Y0.1Fe0.7Mn0.3O3 compound shows uniform growth of grains with less porosity, maximum remanent magnetization (~0.012 emu/g), and enhanced ME coupling coefficient (35 mV/Oe.cm.). The ME coupling coefficient obtained from the optimized sample is six times higher than that of the pristine sample. This work provides a potential route for improving the ME coupling coefficient in BiFeO3- based multiferroic materials for practical applications. 

Abstract

Nanocrystalline Zn1-xCoxO (where x varies from 0 to 0.04 in steps of 0.01) thin films were deposited onto glass substrate by the spray pyrolysis technique at a substrate temperature of 350 °C. The X-ray diffraction patterns confirm the formation of hexagonal wurtzite structure. The crystal grain size of these films was found to be in the range of 11& 36 nm. The scanning electron micrographs show a highly crystalline nanostructure with different morphologies including rope-like morphology for undoped ZnO and nanowalls and semispherical morphology for Co-doped ZnO. The transmittance increases with increasing Co doping. The optical absorption edge is observed in the transmittance spectra from 530 to 692 nm, which is due to the Co2+ absorption bands corresponding to intraionic d-d* shifts. The direct and indirect optical band gap energies decrease from 3.05 to 2.75 eV and 3.18 to 3.00 eV, respectively for 4 mol% Co doping. The electrical conductivity increases with increasing both the Co doping and temperature, indicating the semiconducting nature of these films. The temperature dependence thermal electromotive force measurement indicates that both undoped and Co-doped ZnO thin films show p-type semiconducting behavior near room temperature. This behavior dies out beyond 313 K and they become n-type semiconductors.

Abstract 

Multiferroic (x)Mn0.45Ni0.05Zn0.50Fe2O4+(1-x)BaZr0.52Ti0.48O3materials (where x varies from 0.0 to 0.8 in steps of 0.20) were prepared by the standard solid-state reaction method. X-ray diffraction patterns verify the development of tetragonal perovskite structure for ferroelectric and cubic spinel structure for ferrite phase. The frequency and temperature-dependent electrical parameters have been investigated to understand the conduction mechanism in these multiferroic materials. The grain effect contributes to the conduction mechanism for the sample containing 0–60% ferrite and both the grain and grain boundary effect contribute to the conduction mechanism for the composite containing 80% ferrite at high temperature. The ac conductivity increases with increasing frequency for the sample x=0. This is due to the small polaron hopping. For the sample containing 20% ferrite, the frequency-independent dc conductivity is observed at low temperature and dominates over a wide frequency range at the high-temperature region for the sample containing a higher percentage of ferrite. The frequency-independent dc conductivity is shifted to the frequency-dependent ac conductivity, indicating the beginning of the conductivity relaxation phenomenon. This is attributed to the translation of long-range polaron hopping to the small range charge carriers. The temperature dependence conductivity indicates that the impurities present in these multiferroic materials are almost minimized and polaron hopping type of conduction mechanism is valid. 

Abstract:

In this research, Bi1-xYxFe0.7Mn0.3O3 (x=0.00, 0.05, 0.10, 0.15 and 0.20) ceramics have been prepared by conventional solid state reaction method and sintered at 800, 825 and 875 oC. The prepared samples were characterized by the X-ray diffraction (XRD) analysis, Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray Spectroscopy (EDX). The electrical and magnetic properties were studied using Impedance Analyzer and vibrating sample magnetometer, respectively X-ray diffraction analysis ensured that the parent sample is crystallized in rhombohedra structure and Y- doping generates structural transformation toward orthorhombic structure due to the substitution of Y3+. The bulk density decreases with increasing Y content. The average grain size was found increasing with increasing Y content for sintered temperature 800, and 825oC but decreasing with increasing Y content for sintered temperature 850oC. From EDX analysis, Y content concentrates at the grain boundaries and that is increasing with increasing sintering temperature. Due to space charge polarization dielectric constant was observed to show dispersive behavior at lower frequency. Dielectric constant increased with the increasing Y content. From the impedance and AC conductivity measurement it is observed that the value of impedance decrease with increase in frequency and AC conductivity increased because of hopping of charge carriers. The electrical impedance of compressed disks was investigated by impedance analysis and the results were successfully fitted by a simple parallel R–C model. Impedance spectroscopy also showed that grain and grain boundary contribution is present in the conduction mechanism for x=0.00 and grain boundary resistance is increasing with Y content for x= 0.5-0.20. The real part of complex initial permeability, µi', of the samples increased with sintering temperatures because of uniform grain growth. Magnetoelectric coefficient was observed improving with Y doping in Bi1-xYxFe0.7Mn0.3O3 compositions.