Dielectric and magnetoelectric properties of Li-Mg ferrite: Barium titanate composites

Abstract

The magnetoelectric composites with composition, (y) Li0.45Mg0.1Fe2.45O4 + (1-y) BaTiO3, where, y = 0.1, 0.3, 0.5, 0.7 and 0.9 are prepared by standard ceramic technique. The X-ray diffraction studies revealed the coexistence of two phases without chemical reaction. The dielectric properties are measured at room temperature in the frequency range from 100 Hz to 5 MHz. Same parameters were also measured by changing the temperature from 25 to 500 °C. The dielectric constant initially decreases rapidly with rise in frequency exhibiting dielectric dispersion at lower frequencies and then remains fairly constant at higher frequencies. The dielectric dispersion observed at low frequencies is of the interfacial polarization type and is attributed to various types of polarizations mechanisms. AC resistivity and dielectric constant show a opposite trend of variation with increase in content of ferrite. The variation of dielectric loss with frequency is in analogous to that of dielectric constant vs. Logf. The dielectric constant vs. temperature curves exhibit peaks around two temperatures i.e. one at around 400 K and other at around 725 K which refers to the ferroelectric and ferromagnetic Curie temperatures. The intensity of the peaks at both the transition temperatures decreases as the fixed applied frequency increases. AC resistivity decreases rapidly with rise in frequency initially, then it do not depend on frequency applied. The rapid fall of resistivity at lower frequency is due to increase in the hopping frequency of the electrons between different ionic sites. The linearity in Logσac vs. Logω2 reveals that the conductivity is due to small polarons. ME output increases with rise in dc magnetic field up to the range 2000–2500 Oe and then decreases for further rise in the field. The peaks observed in the ME output curves is attributed to the enhanced domain wall movements near Curie temperature.