Effective conduction-electron-local-moment exchange interaction in metals: Rare-earth interband mixing

The effective diagonal-exchange parameter Jeff(0) which determines the exchange splitting of a metal's Fermi-surface conduction electrons, has been investigated with a model involving simple orthogonalized-plane-wave conduction-electron orbitals and rare-earth ion cores. The positive exchange integral and negative interband mixing contributions to Jeff(0) have been estimated for the rare earths as a function of nuclear charge Z. The results indicate that interband mixing may dominate, causing a net negative conduction-electron polarization, in agreement with a number of experiments. The interband mixing, and hence the sign of Jeff(0), is found to be very sensitive to conduction-electron character. The results also indicate that, for ions other than spherical Gd, the parameter Jeff(0) will vary strongly with conduction-electron k direction (with respect to the J of the rare-earth ion) and may even involve a variation in sign. Such anisotropies in Jeff(0) and the nondiagonal Jeff(Q) parameters should be a significant source of anisotropies in the Ruderman-Kittel-Kasuya-Yosida conduction-electron spin distribution.