Energy-Band Theory of Magnetism

Abstract

Recent progress in energy-band theory leads to the hope that we can understand many ferromagnetic and antiferromagnetic substances from an energy-band point of view. One uses a one-electron approach, with different exchange potentials for electrons with spin up or down. The energy bands can be computed using the augmented plane-wave method, which is well adapted to crystals containing transition elements. Calculations along these lines for Ni and Fe have been made by Wakoh and Yamashita in Toyko, and for Ni by Connolly in Gainesville. Cho, formerly in Gainesville, has treated EuS, a ferromagnetic semiconductor. The method is also adapted to antiferromagnetic crystals, and calculations on several such crystals are under way in Gainesville and Toyko. The significance of the energy separation between the bands for spin-up and spin-down electrons is discussed, for both the ferromagnetic and antiferromagnetic cases. These energy separations are connected with intra-atomic exchange effects, and are much too large to have any direct connection with the Curie or Néel temperatures.