Semiconductivity in Ba2Ni2-xZnxFe12O22Y-type hexaferrites

The electric, thermoelectric and magnetic properties were studied as a function of temperature and composition for a series of Ba2Ni2-xZnxFe12O22 Y-type hexaferrite samples (with x = 0, 0.4, 0.8, 1.2, 1.6 and 2) prepared using the usual ceramic technique. The experimental results indicated that the DC electrical conductivity sigma(DC), thermoelectric power alpha, diff mobility mu(d), carrier concentration n and initial magnetic permeability mu(i) increase whereas the Fermi energy E-F decreases as the temperature increases. alpha has a negative sign for all samples indicating that the majority of electric charge carriers are electrons. The study of initial magnetic permeability showed two peaks on mu(i)-T curves. The first peak nearly appears at Curie temperature T-c for all samples except for the sample with x = 2 while the second peak T-s appears below room temperature for all samples. T-c decreases due to the replacement of non-magnetic Zn2+ ions to magnetic Ni2+ ions, mu(i), activation energies for hopping E-H, for carrier generation E-g and for electric conduction (E-1, E-2 and E-3 in regions I, II and III) decreases to reach minimum at x = 1.2 and start to increase for x > 1.2. Each of sigma(DC), alpha, n, mu(d), and energy at donor level E-D increase as the substitution of non-magnetic Zn2+ ions to magnetic Ni2+ ions increase reaching maximum at x = 1.2 and start to decreases for x > 1.2. The small values of mu(d) and its strong temperature-dependence (exponential relation) indicate that the hopping conduction mechanism is predominant at high temperatures in region III. In region II, the band conduction mechanism shares in electric conduction process beside the hopping conduction mechanism. The band conduction mechanism is predominant in region I. (C) 1999 Elsevier Science B.V. All rights reserved.