INITIAL PERMEABILITY STUDIES ON AL3+ AND CR3+ SUBSTITUTED NI ZN FERRITES

The chemical formula of the samples investigated is Ni0.7Zn0.3Alx/CrxF e2-xO4, where x = 0.00, 0.05, 0.10, 0.15, 0.20 and 0.25. The samples w ere obtained x by x the x usual ceramic technology from high-purity ox ides. The initial permeability was calculated from the inductance meas urements with a torroidal core of 100 turns, using the formula L = 0.0 046 mu iN(2)hlogd(2)/d(1). The initial permeability mu i decreases in Ni0.7Zn0.3Alx/CrxFe2-xO4 with increase in Al3+/Cr3+. The decrease in m u i is attributed to a decrease of grain size D from 4.9 mu m to 4.4 m u m with Al3+ and to 1.9 mu m with Cr3+ and to variations in the aniso tropy constant K-1. The main contribution to the variation of permeabi lity with content of Al3+/Cr3+ in the system is the effect each of the m has on domain wall motion. The trivalent substituents (Al3+/Cr3+) ca use impedance to the domain wall motion, which increases as the conten t of these ions increases. Al3+ has a stronger effect than Cr3+. The i nitial permeability components mu' and mu '' do not exhibit much varia tion with temperature, except near T-c, where they fall sharply. The m aximum of mu '' near T-c has been attributed to a damping effect of do main wall motion. (C) 1998 Chapman & Hall.