The Magnetic properties of iron crystals

Abstract

Comparatively little work has so far been done on the magnetic properties of ferro-magnetic crystals, and it has been confined to substances for which the saturation value of the intensity of magnetisation is small. P. Weiss, the chief worker in this field, did experiments on pyrrhotine, which has a saturation value of 47 absolute units. It is found that, for these crystals, the direction of the magnetisation does not, in general, coincide with the direction of the applied field. To account for this deviation, Weiss postulates a “molecular field” due to the mutual action of the molecules of the crystal. He finds that this molecular field has components along the crystallographic axes, and that for any axis the component of the molecular field is proportional to the component of the magnetisation along that axis. The proportionality factor may vary for different axes. Weiss calculates values for the molecular field, which would account for the deviation of the magnetisation from the applied field, and finds values of the order of 100,000 gauss. It is obviously important to verify the extension of this theory to crystals of iron, which has a much larger saturation value for the magnetisation (about 1,600 abs. units). We have been able to obtain through Miss Elam, of the Imperial College of Science, some crystals of iron large enough for the purpose of the investigation.