Observation of Localized Moments, Kondo Effect, Spin Glass Regime, Magnetic Ordering in Rare Earth System with Unstable Valence

Abstract

Certain rare earth elements have an unstable valence and with compound formation or under pressure exhibit a non-magnetic ground state at low temperature. Their electronic properties are characterized by a very large γT term in their specific heat and a very high Pauli like susceptibility.(1) For example SnB 6 (2) SmS in its collapsed phase (3), αCe (4), CeSn(5), and CeAl 3 (6) are in this nonmagnetic state. This behavior is generally observed on rare earth compounds with an intermediate valence near or far from an integral number which is a clear indication that the 4f level is near the Fermi level, The larger the Pauli-like susceptibility, the nearer the system is to magnetic ordering. Because of the mixing of the 4f level with the conduction electrons the orbital and spin moment (7) of the rare earth can disappear at low temperature or exchange interactions can compete and dominate the Kondo condensation to induce magnetic ordering. As examples we will discuss the case of CeAl2 and CeAl3.