Exchange interactions in magnetic compounds

Abstract

The basic feature of the Heisenberg-Dirac-Van Vleck model of cooperative magnetic phenomena is the assumption that the interaction Vij between a pair of atoms i and j in a crystal has the form Vij=-2J ijSi·Sj, where Jij is an exchange interaction and Si and Sj are spin operators. Such an assumption seems naturally better suited to insulating compounds than to metals and alloys. In principle, it should be possible to determine the J ij for magnetic compounds by comparing experimental data with theoretical predictions based on Eq. (1). In practice, the matter is complicated by the fact that the H-D-VV model is oversimplified, and that even in its oversimplified form exact solutions cannot be obtained for real three-dimensional crystals. The general problem of evaluating exchange interactions in magnetic compounds from experimental data is reviewed, and specific results are presented for some antiferromagnetic and ferrimagnetic systems where a reasonably good determination of the exchange interactions can be obtained. Some correlations and regularities in the data are noted and discussed. A long review article on this topic is being published elsewhere. © 1963 The American Institute of Physics.