Structural distortions in the non-Fermi-liquid system CeCu6-xAux

Full text: CeCu6xAux is a well-known heavy-fermion system in which the ground state is antiferro-magnetically ordered for x > 0.1 and temperatures below 1K. Non-Fermi-liquid behaviour occurs around this critical concentration. The parent compound, CeCu6, shows a structural phase transition near 230K, where it changes from the Pnma orthorhombic room-temperature structure to the P21/c monoclinic structure. The monoclinicity increases as temperature falls, with β reaching 91.44 deg at 10K. Here, powder neutron diffraction at the HIFAR reactor in Australia is used to explore the monoclinicity at 10K as a function of composition for 0.0 < x < 0.08, just short of the critical concentration. Extrapolation of the square of the monoclinic strain, (abcos(β))2, suggests that the distortion vanishes by x = 0.14. At a minimum, the structural distortion and antiferromagnetism seem to be competing with each other, and this raises the intriguing possibility that lattice degrees of freedom are important in the non-Fermi-liquid regime