Apparatus for measurement of velocity of domain boundaries in two dimensions in grain-oriented silicon iron

Disc samples of grain-oriented silicon iron have been subject to rotating magnetic flux, and domains observed by the Kerr effect. Moving patterns at 0.2 Hz were recorded on video tape and the images digitized. The co-ordinates of significant features were logged over several frames and velocities computed from knowledge of the frame count and frame rate. For some grains bar and zig-zag patterns alternate. The transition between these is a rapid sweep across the field of view, its velocity being around ten times that of the bar walls. Bar walls are also created and annihilated. Other grains display variants of this. The flux seems to take selective paths though the grains. Further work with this apparatus should provide data for a model of rotational power loss.