On the Nature of Ferromagnetism in Pyrrohotite

Abstract

The g-value of 0.63 for pyrrhotite indicates that there is a large contribution to the magnetization from orbital moment. The electron density distribution will therefore depend on the direction of magnetization, and the intensity of x-ray reflections from a suitable plane might be expected to show a detectable dependence on this direction. Inglis showed in 1934 that the g-value was consistent with the `carrier' being a d-electron with m1 = + 2, ms = -½. On this assumption calculations have been made of the electronic and atomic form factors (for one effective d-electron per atom) and of the structure factors for reflection on the (110) plane for magnetization normal and parallel to this plane. Although the electronic form factor in the first case is nearly twice as great as in the second, the final calculated difference in intensity is only about 0.83%. A long series of careful intensity measurements has been made, using ionization chamber methods, and the experimental result for the difference is 0.30 ± 0.15%. It is thus shown experimentally that either there is no change in charge distribution with direction of magnetization in pyrrhotite, or the change is much smaller than that indicated by theoretical calculations for the simplest type of model consistent with the experimental g-value.