Specific heat and thermal expansion in U(Pt, Pd)3

Abstract

In UPt3 single crystals the combined Grüneisen parameter analysis of specific heat and thermal volume expansion yields a Kondo type or heavy-fermion contribution (with Γ as high as 73) and, apart from the phonon contribution, another contribution of presumably normal electronic origin (with a Grüneisen parameter equal to 2.2). An analogous combined analysis of the anisotropic part of the thermal expansion (i.e., the ca ratio) and the specific heat yields very much the same contributions. Guided by the knowledge of the Grüneisen parameters for UPt3 we were able to apply the method to U(Pt0.95 Pd0.05)3. Here, an antiferromagnetic long-range contribution can be separated with ΓAF equal to −40. The entropy in this contribution is 1.2 J/mol K, so only 0.2×R ln 2, presumably due to the itinerant nature of the electrons involved in the ordering. Above the ordering temperature the remaining part still can be regarded as a Kondo peak (with TK=6.8 K, instead of TK=22.6 K for UPt3). Below TN the Kondo peak is still present, although somewhat reduced because of the antiferromagnetic order.