Τhe effect of Ni on the magnetic properties of power or high permeability MnZn ferrites

Abstract

In this article an extensive study is presented on the Ni addition in three subcategories of MnZn ferrites under conditions of constant Mn/Zn ratio and Fe excess, namely i) low frequency (∼100 kHz) power ferrites, ii) medium frequency (∼500 kHz) power ferrites and iii) high permeability (μi ∼ 8000, 25 °C) ferrites. As found, Ni is a useful additive for optimizing the high temperature performance of MnZn ferrites since it increases Curie temperature, saturation flux density, magnetic permeability and decreases power losses at temperatures above 100 °C. In addition, the addition of Ni increases the resonance frequency and the frequency stability of the initial permeability and partly counteracts the ageing effects caused by Co, when it is present in medium frequency ferrites. The magnetic results are explained on the basis of Ni-substitutions on octahedral sites associated with a negative contribution to the total magnetocrystalline anisotropy, thereby shifting the temperature at which the magnetocrystalline anisotropy constant K1 changes sign, to higher temperatures. The morphological results are explained assuming that the presence of Ni is associated with decreased cation vacancy and increased anion vacancy concentrations.