Magnetic properties of grain-oriented silicon iron. Part 2: Basic experiments on the nature of the anomalous loss using an individual grain

Measurements of the position of the parallel-bar-domain walls at various points on the magnetising cycle have been made over the frequency range 25¿100 Hz in an individual grain of transformer steel, using the Kerr magneto-optic technique. A single-turn search coil of very thin wire wound around the test grain, through two 0.004 in holes, enabled the flux density to be measured. By plotting the degree of magnetic saturation, as indicated by the position of the surface walls, against the degree of saturation, as measured in the volume by the search coil, the amount of domain-wall bowing could be noted at various frequencies. Even at 25 Hz, there exists considerable bowing. In addition, the total power loss in the same grain has been measured at various flux densities in the frequency range 10¿100 Hz, using the rate-of-temperature-rise technique reported earlier. The importance of carrying out this basic study on a single grain is noted, and the experimental results are discussed in terms of various domain models, and of the various concepts that have been introduced to explain the nature of the anomalous loss.