Enhanced eddy current loss due to domain displacement

Abstract

Magnetization in materials with fine hard co-operative closure-domain structures involves not only the growth of field-favoured domains at the expense of those unfavourably oriented but also considerable displacement and distortion of the surrounding domain structure. Thus the volume swept by domain walls considerably exceeds the increased volume of favourably oriented domains. As micro-eddy currents are generated by all moving domain walls, this co-operative behaviour of complex fine domain structures constitutes an effective source of the enhanced eddy-current damping known to occur in alloys with fine structure in contradiction of the predictions of domain eddy-current models such as that of Pry and Bean. This paper seeks to quantify this phenomenon by calculating the eddy-current dissipation caused by pure displacement of six different characteristic model domain structures. In each case the calculated loss increases with refinement of the structure, the limiting loss per unit volume being (υΔ J) 2/4ϱ, where υ is the velocity of displacement, ϱ is the material resistivity and Δ J is the change in polarization across an interior domain wall.