Experiments on the Nature of Ferromagnetism

Irregularities in the magnetization of ferromagnetic crystals were studied by means of magnetic ${\mathrm{Fe}}_2$ ${\mathrm{O}}_3$ particles about 1μ in diameter suspended in ethyl acetate. On iron crystals the particles settle along parallel lines spaced about 0.1 mm apart and more or less at right angles to the applied field. On nickel crystals the pattern is similar, but the lines split up into more complicated structures as the applied field is increased. On cobalt crystals straight lines are obtained on some crystals, and spotty patterns on others. The spots arrange themselves in rows when the crystals are magnetized. The patterns can be destroyed by relatively slight surface strains. There is some evidence that in the straight line patterns the direction of the lines is related to the direction of magnetization. An explanation of these effects is not known.