Magnetic, dielectric and complex impedance properties of lanthanum and magnesium substituted strontium hexaferrite

Lanthanum and magnesium substituted strontium hexaferrites, having the general formula Sr_1−xLa_xMg_yFe_12−yO₁₉ (x, y = 0, 0.05, 0.10, 0.15, 0.20), have been synthesized by citrate precursor method. X-ray diffraction confirms all the samples exhibit single hexagonal phase with space group P6₃/mmc. The infrared spectrum shows two prominent peaks in the range of 430–590 cm⁻¹ indicating the formation M-type hexagonal ferrite. Magnetic study shows that the value of saturation magnetization and retentivity decreases while as coercivity increases with the concentration of doping. Temperature dependent magnetization presents a sharp peak just below the Curie temperature, showing super-paramagnetic behaviour of the prepared material. The dielectric parameters: dielectric constant, loss, ac conductivity were studied as a function of frequency. The impedance spectroscopy method has been used to analyze the effect of grain and grain boundary on the electrical properties of the prepared material. The Cole–Cole diagram suggests that conduction is mainly due to grain boundaries. La–Mg substitution into strontium ferrite increases the magnetic and dielectric properties which could ensure a higher memory storage capability.