Optical study of Bloch walls dynamics during the magnetization process of Fe-Si G.O. laminations under controlled induction waveform

By using an optical technique, the dynami cal behaviour of local Bloch wall structures characterized by differently spaced antiparallel domains on the same Fe-Si 3% grain-oriented lamination has been invest igated. A previously developed theory of the magnetic power loss in ferromagnetic laminations allows the correlation of the power spectrum of the time derivative of the optical signal with the local magnetic power loss. From this analysis it can be concluded that on a polycrystalline grain oriented material, magnetized under controlled waveform conditions, the local magnetic power loss is weakly dependent on the domain spacing, particularly when the magnetizing frequency is not very small. This effect, which is mainly due to a balancing effect of eddy currents on the Bloch walls speed is also responsible for the so called curvature anomaly of the loss per cycle vs.frequency plot in such materials.