ar X iv : c on d - m at / 0 40 81 91 v 1 [ co nd - m at . s tr - e l ] 9 A ug 2 00 4 Solid state Pomeranchuk effect

Recently we have shown that Y bInCu4 and related compounds present a solid state Pomeranchuk effect. These systems have a first order volume transition where a local moment phase coexists with a renormalized Fermi liquid in analogy with 3 He at its melting curve. We demonstrate here experimentally that the solid state Pomeranchuk effect, controlled by a magnetic field, can be used to produce cooling. The system 3 He along its melting line presents the unusual feature that the entropy of the liquid is smaller than that of the solid [1]. This is the basis of the Pomer-anchuk effect [1] which has an important application as a cooling mechanism and played a central role in the discovery of the superfluid phases of 3 He [1]. It was generally believed that this is a unique property of this extremely quantum system. Recently, we have shown that Y bInCu4 and related compounds also present a solid state Pomeranchuk effect [2,3]. This is best shown in Fig. 1 where at the first order volume transition temperature, TV ≈ 42 K, a local moment phase, indicated by the Curie-Weiss susceptibility,] coexists with a renormalized Fermi liquid with a nearly temperature independent susceptibility, such as along the melting line of 3 He. An external magnetic field shifts the volume instability to lower temperatures according to a law of corresponding states [4,5]. This can be derived from the magnetic Clausius-Clapeyron equation, Fig. 1. Magnetic susceptibility of Y bInCu4 as a function of temperature measured in a field of 1 kOe. At TV ≈ 42 K Fermi liquid and local moment phases coexist. At the coexistence line the magnetization of the local moment phase is much larger than that of the Fermi liquid (MLM ≫ MF L). Also, assuming that the entropies in the distinct phases satisfy the relation SLM ≫ SF L, we get dT dH H V