Dramatic effect of rare earth ion on the electrical and magnetic properties of W-type barium hexaferrites

A series of W-type hexaferrite samples with composition Ba1−yLayZn0.5Mg0.5CoFe16O27; 0≤y≤0.07 were prepared using the solid state reaction to investigate their magnetic properties, AC and DC electrical conductivity and thermoelectric power as a function of composition and temperature. The X-ray diffraction was studied to identify the formation of the sample properly. Increasing of (a) and decreasing of (c) lattice parameters leads to a constant volume. The data of ac conductivity showed an increase with both temperature and frequency, and it becomes slightly independent of frequency at higher temperature, also the conduction mechanism depends on an La concentration. The results of the charge carrier mobility suggested that the hopping conduction mechanism of holes due to replacement of La3+ rare earth ions on the expense of Ba2+ ions is the predominant one. The transition temperature decreases with increasing La content. The values of dc electrical conductivity σdc at room temperature ranged 4.85×10−6–3.82×10−6 (Ω−1 cm−1) and the values of the calculated activation energies Edc ranged 0.215–0.137 eV. The highest values of dielectric constant, electrical conductivity and Curie temperature, also the smallest value of porosity and effective magnetic moment are found at y=0.05. The thermoelectric power coefficient showed that the majority of charge carriers are P-type, except at y=0.03, 0.04 and 0.05 negative charge carriers (electrons) takes place at high temperature region.