Multiferroic iron doped BaTiO3 nanoceramics synthesized by sol-gel auto combustion: Influence of iron on physical properties

Abstract

Iron (Fe) doped barium titanate nanoceramics (BaTi1-xFexO3) were synthesized through sol-gel auto combustion route. The effect of Fe doping on the structural, morphological, ferroelectric and magnetic properties was systematically studied. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopic measurements showed that the synthesized samples have a tetragonal dominant structure with the presence of intermediate hexagonal phase for higher Fe content (x=0.4 and 0.5). Accurate values of average crystallite size (D) and lattice parameter (a and c) were calculated by the Williamson-Hall (W-H) analysis and Nelson-Riley extrapolation function (N-R) respectively. The calculated average crystallite size (D) of the prepared samples is in the 17–27nm range. The surface morphology of the grains was examined by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Compositional stoichiometry was confirmed by energy dispersive spectrum (EDS) analysis. The ferroelectric property was studied by a P-E hysteresis loop. Magnetic and ferroelectric hysteresis loops are strongly influenced by Fe ion doping concentration due to creation of oxygen vacancies. The saturation electric polarization decreases with the increasing of Fe ion doping concentration. The pure BaTiO3 prepared exhibits diamagnetism. Simultaneously, magnetization of doped compositions is enhanced with increasing of Fe ion concentration. Room temperature ferromagnetism is also observed in Fe doped BaTiO3 samples. This anomaly in the magnetic behavior can be explained in terms of the changes in the oxidation state exchange interactions of ions such as the Fe3+-to-Fe4+ change induced by oxygen vacancies. A divergence was observed in the temperature dependence of the field cooling (FC) and zero-field cooling (ZFC) magnetization curves, indicating a spin-glass behavior arising from micro-magnetic state, i. e. the mixing of ferromagnetic and antiferro-magnetic phases. The ferromagnetic properties are predominant below 50K and increases with the Fe doping concentration.