Electric and magnetic properties of Y-type Ba2Mg2Fe12O22 hexaferrites with various Co doping

Abstract

Y-type hexaferrites Ba2Mg2−x Co x Fe12O22 (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 Fe3+ and Fe2+ as well as the hole hopping between Co2+ and Co3+ 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 Co2+ 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 Mg2Y type hexaferrite, which is essential for microwave and electronic applications in the materials.