Heisenberg superexchange

And the combination of Heisenberg superexchange plus Zener double exchange results in zero-field energy levels in terms of the system spin S... 

Note that, at least in a first approximation, all superexchange interactions are confined to the 60 edges of the Fe30 icosidodecahedron and that all Heisenberg interactions are characterized by a single exchange constant. 

This relationship, known as Bloch s rule, applies in the localized-electron limit where the interatomic spin-spin interaction is described by the superexchange perturbation theory of eq. (23) with 7n J J is the Heisenberg exchange energy. Calculations by Shrivastava and... 

The relative signs of and were felt to be in reasonable accord with the Cu-Cl-Cu (—90°) and Cu-(/i,4-0)-Cu superexchange pathways. A recently reported example (271), [Cu40(Cl)g(benzimidazole)4], displayed IX values which, like the py complex, were essentially independent of temperature, except for a decrease at very low temperatures. They should provide a good test for Lines theory (269) vis-a-vis Heisenberg theory. 

---