Structural, magnetic, dielectric and optical properties of the Eu2Bi2Fe4O12 bismuth-based low-temperature biferroic

Abstract

The monophasic polycrystalline ceramic perovskite-based Eu2Bi2Fe4O12 was synthesized by the solid-state reaction method. X-ray diffraction measurements in the Bragg–Brentano geometry and Rietveld analysis reveal that this material crystallizes in an orthorhombic structure with Pnma (#62) space group. Average grain size of 450 nm is calculated of a log-normal distribution and obtained by means scanning electron microscopy images. Results from magnetization, pyroelectric and complex impedance measurements as a function of temperature (50 K up to 300 K) show the occurrence of dielectric and magnetic relaxation process starting simultaneously at 112.8 K. The tendency of real and imaginary curves of the dielectric permittivity at temperatures close to room temperature has also shown strong ac conductivity contributions attributed to porosity effects. The magnetization hysteresis loop at room temperature confirms that this new perovskite-based material has a ferromagnetic response. Signature of superparamagnetism effects is also observed as a consequence of the nanometric grain size. Thermostimulated current measurements as a function of temperature reveal the occurrence of ferroelectric polarization for the temperature regime below T = 112.8 K. Diffuse reflectance experiments permitted to establish the semiconductor nature of this material at room temperature with an energy gap of 2.65 eV.