Valence instability in antiferromagnetically ordered 4f systems

Abstract

An extended s-f model is used in order to study the stability of collective magnetic order in 4f systems which have antiferromagnetic ground states in the normal-valence phase and fluctuate between a magnetic and a non-magnetic configuration in the intermediate-valence phase. The local magnetic 4f moment mf is discussed in terms of the hybridisation V and f-level position Ef, which simulates the influence of external pressure or of alloying with proper impurities. Increasing V and reducing the gap by shifting Ef towards the conduction band intensity electronic fluctuations leading to a partial or even total quenching of the local f moment in the intermediate-valence phase. Corresponding phase diagrams are derived and discussed. The authors observe magnetic first-order transitions from a highly polarised antiferromagnetic state into th non-magnetic state or into a less polarised antiferromagnetic state. In the latter case the final transition into the non-magnetic state is then of second order. The magnetic behaviour is a direct consequence of the sensitive reactions of the quasiparticle densities of states to the variations in Ef and V. This is illustrated by some typical examples.