Impedance spectroscopy and magnetic properties of Mg doped Y-type barium hexaferrite

Single phase samples of Mg doped Y-type hexaferrites with a composition of Ba₂(Co_1−xMg_x)₂Fe₁₂O₂₂ for x = 0–0.5 were prepared using the solid state route. The values of lattice constant and the unit cell volume are found to decrease systematically with increase in Mg concentration. The analysis of impedance spectra and the thermal activation of relaxation process show the contributions from both grains and grain boundaries with decrease in activation energies as Mg concentration is increased. The complex impedance spectra show a deviation from an ideal Debye type and they are modelled using an equivalent circuit consisting of resistances of grains and grain boundaries, grain capacitance and a constant phase element. However at higher temperature (T ≥ 573 K), the contribution of electrode resistance is also taken into account. The analysis of electrical conductivity data show that it is controlled by small polaron tunneling model. The magnetization measurements show that the saturation magnetization marginally decreases from 26.6 emu/g for x = 0–22.7 emu/g for x = 0.5 along with decrease in ferrimagnetic transition temperature from 613 to 581 K.