On the theory of ferromagnetism (by Hesisenberg and translated by Delphenich)

By W. Heisenberg in Leipzig

The original title " Zur Theorie des Ferromagnetismus "

Translated by D. H. Delphenich

 Abstract

WEISS’s molecular forces will be attributed to a quantum-mechanical exchange phenomenon, and indeed, it will be treated as the exchange process that was successfully enlisted in recent times by HEITLER and LONDON in order to interpret homopolar valence forces


Introduction. Ferromagnetic phenomena have be interpreted in a formally satisfying way by the well-known WEISS theory (* ). That theory is based upon the assumption that every atom in a crystal experiences a directed force from the remaining atoms of the lattice that should be proportional to the number of already-directed atoms. By contrast, the origin of these atomic fields was unknown, and several obstacles stood in the way of any interpretation of the WEISS forces on the basis of classical theory: Magnetic interactions between atoms are always a few orders of magnitude smaller than the atomic fields that follow from ferromagnetic experiments. Indeed, electric interactions lead to the correct order of magnitude; however, one would rather expect that the electrical interactions of two atoms would be proportional to the square of the cosine of their mutual angle of inclination, rather than the cosine, which contradicts the assumptions of WEISS’s theory. Other complications were discussed more thoroughly by LENZ (**), and ISING (***) succeeded in showing that the assumption of directed, sufficiently large forces between any two neighboring atoms of a chain did not suffice to generate ferromagnetism.

http://www.neo-classical-physics.info/uploads/3/4/3/6/34363841/heisenberg_-_on_the_theory_of_ferromagnetism.pdf