The Bitter method is most commonly observing way of the magnetic domains situation even though it is possible to observe only the surface of specimen. Applying magnetic field to this magnetic material covered by magnetic fluid makes it possible to observe the magnetic domain dynamics by a microscope.This paper reveals that the parts exhibiting 1/f fluctuation frequency characteristic give high the iron loss while not exhibiting 1/f fluctuation parts, i.e. containing much silicon, give low iron loss. Thus, it is revealed that the mixture rate of iron and silicon determines the optimal silicon steel composing most of the electrical machines
