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) 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.