Magnetostriction and the phenomena of the curie point

Abstract

Section 1. Introduction .—Heisenberg’s theory of ferro-magnetism claims no more than to show us the nature of the origin of this phenomenon—that is to say, where it will be found in the quantum-mechanical theory of a solid when the necessary complicated calculations can be made. He shows that it arises from the exchange degeneracy of the electrons in the different electronic systems of the lattice, and the modest claims he makes for his theory will be acknowledged by everyone. In spite of the crude stage of present development, which we are not in a position to improve, we may perhaps be allowed to embroider a little round Heisenberg’s theme. In reflecting on his theory we have tried to see whether it can also provide a natural home for the associated phenomena of the Curie point and for magnetostriction. The thermal phenomenon of recalescence has already been incorporated by Weiss in his theory. Since Heisenberg’s contribution is merely to explain the origin of Weiss’a molecular field, his theory will naturally be expected to account for the large change of specific heat on passing through the Curie point, which is the essence of the phenomenon of recalescence. We shall, therefore, merely call attention at a later stage to the origin of this extra specific heat and note how satisfactorily it fits into Heisenberg’s theory. On the other hand, there has hitherto been no theory or of the phenomena of magnetostriction, nor has any theoretical relation been traced between them. Both these effects, notably the former, are far too large to be explained by magnetic forces, just as the normal magnetic forces between the systems of the metallic lattice can only provide fields which are insignificant compared with Weiss’s molecular field. It is almost obvious that the exchange effects of Heisenberg’s theory of ferromagnetism must also explain these changes of volume. There is no reasonable alternative.