Electric and magnetic properties of Y-type Ba_2Mg_2Fe_(12)O_(22) hexaferrites with various Co doping

摘要

Y-type hexaferrites Ba_2Mg_(2-x)Co_xFe_(12)O_(22) (x = 0.4, 0.8, 1.2, 1.6) were synthesized by solid state reaction method. The impedance spectrum, AC conductivity, and dielectric properties were investigated at various temperatures and in a wide range of frequency. The dielectric properties and AC conductivity have been explained on the basis of space charge polarization and the electric exchange between Fe~(3+) and Fe~(2+) as well as the hole hopping between Co~(2+) and Co~(3+) ions at octahedral side. The complex impedance analysis indicates the existence of space charge and the presence of electrical processes at increased temperatures. The change of the activation energy obtained from lnf_(max) versus 1/T and lnσ_(dc) versus 1/T plots indicated that with increasing Co content, the transport mechanisms at low and high temperatures are different. Two magnetic phase transitions were observed in these samples and their transition temperatures increased with increasing Co~(2+) doping. High Co content suppresses the second magnetic structure transition under an applied magnetic field. For all samples, the room temperature coercivity is less than 20 Oe, while the saturation magnetization increases with increasing Co content. The present work provides a fundamental understanding of the dielectric and conductivity mechanism of Mg_2Y type hexaferrite, which is essential for microwave and electronic applications in the materials.