Interplay of magnetism and valence instabilities in lanthanide systems

José Luiz Ferreira,Claudine Lacroix,Sébastien Burdin

doi:10.1016/j.jsamd.2016.06.007

Abstract

Abstract The valence instability in lanthanide systems is described within an extended periodic Anderson Hamiltonian (EPAM) which includes Coulomb repulsion between f- and conduction- electrons, allowing to describe both discontinuous and continuous valence variations. We investigate the connection between valence and magnetism in this model and show that it can be applied to several lanthanide compounds showing both magnetic and valence instabilities.

Highlights

Intermetallic lanthanide compounds are usually classified into normal and anomalous rare earth systems
We Study an Extended Periodic Anderson Model (EPAM) which can be written in the following form:
The model proposed in this paper shows that magnetic and valence instabilities are strongly connected since in most cases, valence fluctuations occur between a magnetic and a non-magnetic valence state

Summary

Introduction

Intermetallic lanthanide compounds are usually classified into normal and anomalous rare earth systems. The valence of the rare earth is well defined (usually 3þ), the magnetic moment is determined by Hunds rules and crystal field interactions, and RKKY exchange interactions are responsible for magnetic order. There are compounds in which this scheme fails; such anomalous systems are often observed with Ce, Yb, Eu, Sm or Tm. In this paper we are interested in compounds in which the valence may change with pressure, magnetic field, or doping. In this paper we are interested in compounds in which the valence may change with pressure, magnetic field, or doping Such valence change is accompanied by a change of the 4f-magnetic moment, and in many cases (Ce, Sm, Eu or Yb) one of the valence state is nonmagnetic. This paper presents a model based on an extension of the Periodic Anderson Model that includes inter-orbital Coulomb repulsion appropriate to discuss the interplay of magnetic and valence transitions in such compounds

Model and approximations

Magnetism and valence

Conclusions