抄録
The Néel temperature, TN, where the energy gap, g, tends to zero is calculated. A flow of electrons between the octahedral Fermi surfaces of the electron and hole bands and the other free Fermi surfaces (called the reservoir) is taken into account. It is shown that the Fermi energy depends appreciably on temperature due to the flow of electrons, so that the calculated TN is different from that given in a previous paper where the temperature-dependence of the Fermi energy neglected. However, the overall agreement with experimental results is found still satisfactory. The order of the phase transition is studied by calculating dg2⁄dT at TN. It is found that although dg2⁄dT changes considerably with the density of states of the reservoir, this change is not large enough to bring out first-order transition. Finally, a comment is made on a related theory proposed by Mitsudo et al.
