Dielectric and magnetic properties of Mg–Ti substituted barium hexaferrite

Barium hexaferrites with general chemical formula BaFe12−2xMgxTixO19 (x=0, 1, 1.5, 2) were synthesized by the solid state diffusion method. X-ray diffraction (XRD) confirmed the formation of single phase magnetoplumbite with large crystallite size. The lattice parameter a decreased with the increase in x, leading to the increase in X-ray density. Formation of well defined grains was observed through scanning electron microscopy (SEM). The dielectric properties were studied by impedance measurements as a function of frequency (in the range 100Hz–10MHz) and temperature (in the range 30°C–345°C). The effect of composition, frequency and temperature on the dielectric constant (ε′), dielectric loss (tan δ), and conductivity (σ) have been explained on the basis of hopping of electrons between Fe2+ and Fe3+ ions. The variation of magnetization (M) with applied magnetic field (H) and temperature (T) were studied with a vibrating sample magnetometer (VSM). The coercivity (Hc) and saturation magnetization (Ms) decreased with the substitution level due to the occupancy of Ti4+ ions at octahedral site and of Mg2+ ions at tetrahedral site. Superparamagnetic behavior was observed in the compounds with x=1.5 and 2. Curie temperature decreased with the increase in x as some intersublattice exchange interactions strongly decreased with Mg and Ti addition.