Correlations in rare-earth transition-metal permanent magnets

Abstract

It is investigated how electron-electron correlations affect the intrinsic properties of rare-earth transition-metal magnets. Focusing on orbital moment and anisotropy, we perform model calculations for 3d-4f alloys and density-functional theory (DFT) calculations for NdCo 5 . On an independentelectron level, the use of a single Slater determinant with broken spin symmetry introduces Hund's rule correlations, which govern the behavior of rare-earth ions and of alloys described by the local spin density approximation (LSDA) and LSDA þ U approximations to DFT. By contrast, rareearth ions in intermetallics involve configuration interactions between two or more Slater determinants and lead to phenomena such as spin-charge distribution. Analyzing DFT as a Legendre transformation and using Bethe's crystal-field theory, we show that the corresponding density functionals are very different from familiar LSDA-type expressions and outline the effect of spin-charge separation on the magnetocrystalline anisotropy. V C 2015 AIP Publishing LLC.

Anisotropy and orbital moment in Sm-Co permanent magnets

“…It has been argued that DFT is able to predict the correct ground-state energy of any magnetic system, but the Sm anisotropy involves excited states (J mixing), and the density functional for combined 3d-4 f systems is not known. In cases where the density functionals for highly correlated systems are known [57,58], the functionals look actually very different from LSDA(+U) density functionals.…”