A model of initial permeability of soft ferrite in dependence of biaxial stress

Abstract

The topic is the interpretation of measured values, a theoretical model and the investigation of critical parameters affecting stress sensitive permeability. The computer aided biaxial compression testing device allows the determination of the permeability, while at the same time the applied stress is measured. Compressive stress vertical to magnetisation is an equivalent to tensile stress parallel to magnetisation and vice versa. The rise of permeability can be found in a crystal anisotropy which is partly compensated by increasing magnetostrictive energy density. After reaching a maximum, the rising magnetostrictive energy leads to a monotonous decrease of permeability. The composition of ferrite and direction of stress strongly affects the stress sensitivity. Structural defects such as microcracks and rough edges result in giant local stress, which drastically reduces the initial permeability. A stress insensitive iron deficit MnZn ferrite is found (μi=500). Furthermore, stress induced μ(s)-hystereses are measured and theoretically explained.