Electron correlation in transition metals

Abstract

Abstract The role played by electron correlation in determining the magnetic properties of transition metals is reviewed. The successes of band theory, local spin density functional methods and the random phase approximation are discussed. These include calculations of electron and spin density distributions, the form of the Fermi surface, the spin susceptibility at T = 0 and spin wave energies. However, it is shown that the energy dependence of the self-energy, not included in a local potential, is important for determining quasi-particle energies away from the Fermi surface, such as the top of the majority spin band in nickel. This energy dependence is also essential for understanding the low temperature behaviour of the spin susceptibility of paramagnetic metals. The transition to a Curie-Weiss law at higher temperatures is discussed. The experimental observation of spin waves above the Curie temperature in ferromagnetic metals indicates long range spin correlations which may be understood in nickel using a model of three quasi-two-dimensional sub-bands. A new approach to very weak itinerant-electron ferromagnets, based on Hund's rule interactions between strongly-correlated paramagnetic sub-bands, is outlined.