High-resolution x-ray diffraction study of the heavy-fermion compound YbBiPt

Abstract

<p>YbBiPt is a heavy-fermion compound possessing significant short-range antiferromagnetic correlations below a temperature of T*=0.7K, fragile antiferromagnetic order below TN=0.4K, a Kondo temperature of TK≈1K, and crystalline-electric-field splitting on the order of E/kB=1–10K. Whereas the compound has a face-centered-cubic lattice at ambient temperature, certain experimental data, particularly those from studies aimed at determining its crystalline-electric-field scheme, suggest that the lattice distorts at lower temperature. Here, we present results from high-resolution, high-energy x-ray diffraction experiments which show that, within our experimental resolution of ≈6–10×10−5Å, no structural phase transition occurs between T=1.5 and 50K. In combination with results from dilatometry measurements, we further show that the compound's thermal expansion has a minimum at ≈18K and a region of negative thermal expansion for 9≲T≲18K. Despite diffraction patterns taken at 1.6K which indicate that the lattice is face-centered cubic and that the Yb resides on a crystallographic site with cubic point symmetry, we demonstrate that the linear thermal expansion may be modeled using crystalline-electric-field level schemes appropriate for Yb3+ residing on a site with either cubic or less than cubic point symmetry.</p>