Unusual magnetic anisotropy of Si-poor FeNbCuBSi alloys

Abstract
If compared to ribbons of standard FeNbCuBSi (13÷16.5 at.% Si) nanocrystalline alloy, different annealing behaviour is displayed if the above alloy contains 10 and less at.% of Si. The most striking difference is observed on samples annealed/nanocrystallized in an atmosphere (e.g. Ar), where the hard direction is aligned along the ribbon's long axis. The particular annealing behaviour of magnetic anisotropy varies with Si contents, with annealing time and yet it differs for vacuum annealing. These peculiarities are studied on a series of Si-poor FeNbCuBSi alloys by magnetic measurements and Mössbauer spectroscopy, consulting DSC and density measurements as well. Some of the abundant problems are discussed in detail in this work. The main idea to explain the behaviour is based on a squeezing-surface effect which results in forming of magnetoelastic as well as of stress induced anisotropy.