Magnetic Properties of Magnetite Crystals at Low Temperature

Abstract

Thin circular disks cut parallel to the 100, 110 and 111 planes of magnetite crystals were prepared. The components of the intensity of magnetization normal and parallel to the magnetic field at temperatures down to that of liquid air were investigated by the method of torsion. It was found that the magnetic properties of the crystal abruptly changed at about -160°C. This temperature corresponds exactly to the temperature at which the specific heat of magnetite increases suddenly to a maximum as was found by Millar two years ago. X-ray photographs taken at room temperature and at liquid air temperature show no difference indicating that there is no change in the distribution of the points of diffraction. The intensity of the two patterns requires further measurements. Weiss' theory of the molecular field cannot be applied as -160°C is not a Curie point.