The variation of domain wall motion throughout the magnetization cycle in grain-oriented silicon-iron

The excess eddy current loss, formerly called the anomalous loss, is, in modern grain-oriented 3% silicon-iron, responsible for about 50% of the total loss for the power frequency range. Hence, it is commercially important for the causes of the excess eddy current loss to be defined. One of the suggested possible causes of the excess eddy current loss is non-sinusoidal, non-uniform and non-repetitive domain wall mobility from the ideal behaviour. In the study reported here, the domain wall positions have been measured in individual grains in commercial polycrystalline 3% grain-oriented silicon-iron for peak flux densities of up to 1.2 T and over a frequency range of 20 to 120 Hz. The flux density of the individual grain is maintained sinusoidal by the feedback technique and by restricting the peak flux density to 1.2 T the observed domain wall motions are completely repetitive. The domain wall motions have been observed using a double-sided stroboscopically illuminated Kerr magneto-optic effect bench which enables the domain structure, spacing and mobility, to be measured on both sides of the sample simultaneously. The position of the domain walls have been measured throughout the magnetization cycle. It is shown that the movement of the walls is not sinusoidal, although the localised flux density is sinusoidal. It is also shown that the wall motions are complex since the amount of domain wall bowing varies throughout the magnetization cycle.