MAGNETISM IN RARE-EARTH-METALS AND RARE-EARTH INTERMETALLIC COMPOUNDS

Some of our recent local spin density electronic structure calculations for a number of ferromagnetic rare-earth systems are reviewed. A simplified model of the level densities for rare-earth (R) transition metal (M) intermetallic compounds, R(m)M(n), is used to describe in a simple way the main features of their basic electronic structure. Explicit calculations for LuFe2 and RFe2 (R = Gd-Yb) systems are presented, where a method to treat simultaneously the localized 4f and the conduction electron spin magnetism is introduced. Thereby it becomes possible to calculate the K(RM) exchange coupling constant. This method is also used to study theoretically the permanent magnet material Nd2Fe14B. The electronic structure of the anomolous ferromagnets CeFe2 and CeCo5 is discussed and an induced 4f itinerant magnetism is predicted. The gamma-alpha transition in cerium metal is considered, and results from calculations including orbital polarization are presented, where a volume collapse of 10% is obtained. On one side of the transition the 4f electrons are calculated to be essentially non-bonding (localized) and on the other side they are found to contribute to the metallic bonding and this difference in behaviour gives rise to the volume collapse. Recent calculations by Wills, Eriksson and Boring (Ref. [5]) for the crystal structure changes in cerium metal under high pressure are discussed. Their successful results imply an itinerant picture for the 4f electrons in alpha-cerium. Consequently this strongly supports the view that the gamma-alpha phase transformation is caused by a Mott transition of the 4f electrons.