The Magnetic Structure of Iron Crystals

A number of powder patterns found on demagnetized strain-free crystals of silicon-iron of known orientation are illustrated and discussed. The specimens were cut from strips of transformer steel in which fairly large crystals had been grown by the strain-anneal method. Smooth undamaged surfaces were prepared by electrolytic polishing. A magnetic field of only 10 oersteds applied normal to the specimens was sufficient to produce patterns; the intensity of the stray fields must thus be of this order of magnitude. On account of the large demagnetization factor ($4\pi$) of the specimens, the patterns are characteristic of the demagnetized state. All evidence points to a layer magnetization with alternate layers oppositely magnetized. The thickness of the layers in different specimens ranged from 10 to 50 microns. Superposed on this primary layer magnetization was a finer secondary structure, presumably localized near the crystal surface, and attributable to dendrite-like regions of reversed magnetization which reduce the magnetic energy associated with the surface stray fields.