LOCAL-BAND THEORY OF ITINERANT FERROMAGNETISM .4. EQUIVALENT HEISENBERG-MODEL

The main results of the picture of itinerant ferromagnetism previously presented are obtained by the functional-integral method of Stratonovitch and Hubbard. A new form of this technique is introduced which is spin rotationally invariant in all approximations and which respects the Pauli principle. By a generalization of the saddle-point method, the itinerant-electron thermodynamics is transformed to that of a classical Heisenberg model with Ruderman-Kittel exchange. © 1979 The American Physical Society.