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

TL;DR

This study uses high-resolution x-ray diffraction to investigate the structural properties of YbBiPt, a heavy-fermion compound, finding no structural phase transition between 1.5 and 50 K and analyzing thermal expansion behavior.

Contribution

It provides the first high-resolution x-ray diffraction data showing no structural phase transition in YbBiPt within the studied temperature range and models thermal expansion with crystalline-electric-field schemes.

Findings

No structural phase transition between 1.5 and 50 K.

Thermal expansion shows a minimum at ~18 K and negative expansion between 9 and 18 K.

Lattice remains face-centered cubic at 1.6 K.

Abstract

YbBiPt is a heavy-fermion compound possessing significant short-range antiferromagnetic correlations below a temperature of $T^{\textrm{*}}=0.7$ K, fragile antiferromagnetic order below $T_{\rm{N}}=0.4$ K, a Kondo temperature of $T_{\textrm{K}} \approx1$ K, and crystalline-electric-field splitting on the order of $E/k_{\textrm{B}}=1\,\textrm{-}\,10$ K. 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 $\approx6\,\textrm{-}\,10\times10^{-5}$ \AA, no structural phase transition occurs between $T=1.5$ and $50$ K. In combination with results from dilatometry measurements, we further show that the compound's thermal expansion has a minimum at $\approx18$ K and a region of negative thermal expansion for $9<T<18$ K. Despite diffraction patterns taken at $1.6$ K 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 Yb$^{3+}$ residing on a site with either cubic or less than cubic point symmetry.