Magnetic ordering in strongly correlated-electron uranium systems:: Consequences of two kinds of f-electron-band-electron states

Magnetic ordering involves the electronic behavior globally; and for uranium-based systems, the hybridization-induced effects dominate over the Coulomb exchange effects in determining the magnetic ordering. Therefore, as long as the hybridization is treated as acting between properly exchange-symmetrized two-electron wave functions, the effects of exchange can be incorporated in the one-electron exchange-correlation potential. As a consequence of the necessary exchange symmetrization, there are essentially two kinds of f electrons, localized magnetic and itinerant nonmagnetic. This has enabled us to make absolute material-specific predictions of alloying or high-pressure effects on magnetic ordering in uranium strongly correlated-electron (SCE) systems using local-density approximation input into many-electron dynamics. Experimentally, the alloying effects can be dramatic, e.g., in UxLa1-xS the magnetic ordering abruptly disappears at about 55% uranium. The theory is quite successful in its detailed absolute predictions, and this has important implications for the overall understanding of electronic behavior in SCE systems including heavy fermion systems. The key conclusion is that strengthening the hybridization, as kinematically restricted by exchange symmetry, leads to a chemical-environment-dependent sharp phase transition in SCE systems with dramatic observable consequences. This phase transition is associated with the elimination of the localized-magnetic transition-shell electrons (f electrons for light actinide and cerium-based SCE materials, d electrons for transition-metal-oxide-based SCE materials). (C) 1999 American Institute of Physics. [S0021-8979(99)16908-1].