LXVIII. Interchange interaction and collective electron ferromagnetism

Summary A preliminary discussion is given of the interchange interaction energy terms occurring in the collective electron treatment of ferromagnetism. The theoretical background is outlined (§ 2) and the relevant energy terms calculated for free electrons (§ 3). I t is shown that, if the interchange interaction energy for anti-parallel spins is taken into account qualitatively, the total energy may vary as the square of the magnetization, as is assumed in Stoner's statistical treatment (1938). Application to electrons in actual metals will require some very complicated calculations; a brief outline is given (§ 4) of the three main approximational methods which may be used. Valuable information may, however, be obtained by careful analysis of experimental results (§ 5); a possible explanation may, for example, be given of the discrepancy between the calculated and observed magnetization, temperature curve of nickel. It is finally suggested (§ 6) that the collective electron treatment provides a much more satisfactory approach to the problems of ferromagnetism than the Heitler-London-Heisenberg method.