The magnetism of iron

A type of theory capable of reconciling the localized- and itinerant-electron models of a ferromagnetic metal is discussed. This kind of theory contemplates a distribution of "exchange field" configurations which correspond very roughly to the spin configurations of the localized model. Computations involve thermal averages over these configurations, each configuration $V$ having an effective energy $E\left(V\right)\mathrm{}$. Starting from the band structure for ferromagnetic iron, the $E\left(V\right)\mathrm{}$ have been estimated for certain configurations $V$. The results are reasonably consistent with the observed Curie temperature of iron, in spite of the presence of exchange fields ∼1-2 eV, and give some suggestion of behavior characteristic of the Heisenberg model.