High Field Magnetization, AC Susceptibility and Thermoelectric Power Studies of Pb4+ Substituted Nickel Ferrite

Abstract

A series of polycrystalline spinel ferrites with composition Ni_1+xPb_xFe_2-2xO₄, x= 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5 were prepared by the standard ceramic method.  X-ray diffraction pattern of the sample revealed single phase cubic spinel structure. The magnetic properties were investigated by means of high field magnetization and ac susceptibility. The transport properties were studied by thermoelectric power measurement. Magnetization measurement showed that increase in the magnetization as Pb⁴⁺ concentration upto x= 0.1 and then it decreases with addition of Pb⁴⁺ concentration. Ac susceptibility was measured from room temperature to the Curie temperature (T_c) of the sample. Variation of ac susceptibility with temperature showed that the sample with X= 0.0, 0.1 and 0.2 contain single domain (SD) particles where as the sample with x= 0.3, 0.4 and 0.5 shows multi domain nature (MD).  The values of Curie temperature (T_c) as obtained from study of variation of ac susceptibility with temperature were found to decrease with increase in the Pb⁴⁺ concentration (x). The compositional variation of thermoelectric power shows n-type behaviour for the sample x = 0.0, 0.1 and 0.2 where as p-type behaviour for the samples x ³ 0.3 upto temperature 521⁰K. Then p to n transition is observed. This p to n transition is attributed to formation of Ni³⁺ and Fe³⁺ ions. The temperature dependence of seebeck coefficient (a) clearly confirm the conduction mechanism due to polaron hopping.