The Breakdown of Normal Magnetic Order in Rare Earth Metals

Abstract

It is generally believed that the major features of systems described as intermediate valent, heavy fermion or Kondo lattice can be understood on the basis of the Anderson lattice. Many such systems do not order magnetically; on the other hand the Anderson lattice can also describe a normal rare earth metal in which the 4f electrons behave as localized moments which order in the ground state. Clearly the Anderson lattice undergoes a phase transition from a magnetic to a non-magnetic ground state as the hybridization of the 4f states with the conduction band is increased. Most theoretical work>1 which has been done on this transition approaches it from the non-magnetic side. In this paper we start with the magnetic state of a normal rare earth metal and investigate its instability as the hybridization strength increases. For simplicity we assume that the magnetic state is a ferromagnetic one, as in Gd or the majority of RAl2 compounds. We neglect orbital degeneracy1 of the f level; this is not unreasonable for a Ce system (approximately f) where the crystal field may produce a doublet ground state. We might consider that with weaker hybridization, in an expanded lattice for example, CeAl2 be a normal ferromagnetic rare earth metal and that its reduced and modulated moment>2 are symptoms of the onset of instability of this normal state.