Homogeneity of Magnetic Properties Within a Single Soft Magnetic Core, Especially in Huge Cores

Abstract

Soft magnetic cores made of nanocrystalline FINEMET-type <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">$({\rm Fe}_{73,5}{\rm Cu}_{1}{\rm Nb}_{3}{\rm Si}_{15,5}{\rm B}_{7})$ </tex-math></inline-formula> ribbon have never been studied whether they are homogenous regarding their magnetic and mechanical properties. For small cores (i.e., cores with thin wall thickness), this is not so much in doubt as for heavy cores (e.g., <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">${\sim}{\rm 2}~{\rm kg}$ </tex-math></inline-formula> with 46 mm wall thickness). As it is well known, during the annealing process, this mass cannot be heated uniformly in normal industrial conditions, which causes differences regarding the magnetic and mechanical properties between the samples taken from various parts of the core. In this paper, we demonstrate that high inhomogeneity exists within a single toroidal core in terms of its magnetic properties. The measurement method and the experimental results are described in detail.