Initial permeability studies on A13+ and Cr3+ substituted Ni–Zn ferrites

Abstract

The chemical formula of the samples investigated is Ni0.7Zn0.3Alx/CrxFe2-xO4, where x=0.00, 0.05, 0.10, 0.15, 0.20 and 0.25. The samples were obtained by the usual ceramic technology from high-purity oxides. The initial permeability was calculated from the inductance measurements with a torroidal core of 100 turns, using the formula L=0.0046 μiN2h log d2/d1. The initial permeability μi decreases in Ni0.7Zn0.3Alx/CrxFe2-xO4 with increase in Al3+/Cr3+. The decrease in μi is attributed to a decrease of grain size D from 4.9 μm to 4.4 μm with Al3+ and to 1.9 μm with Cr3+ and to variations in the anisotropy constant K1. The main contribution to the variation of permeability with content of Al3+/Cr3+ in the system is the effect each of them has on domain wall motion. The trivalent substituents (Al3+/Cr3+) cause impedance to the domain wall motion, which increases as the content of these ions increases. Al3+ has a stronger effect than Cr3+. The initial permeability components μ′ and μ″ do not exhibit much variation with temperature, except near Tc, where they fall sharply. The maximum of μ″ near Tc has been attributed to a damping effect of domain wall motion. © 1998 Chapman & Hall