Abstract
CeCu 6− x Au x is a well-known heavy-fermion system in which the ground state is antiferromagnetically ordered for x>0.1 and temperatures below 1 K. Non-Fermi liquid behaviour occurs around this critical concentration. The parent compound, CeCu 6, exhibits a structural phase transition near 230 K, where it changes from the Pnma orthorhombic room-temperature structure to the P2 1/c monoclinic structure. The monoclinicity increases as temperature falls, with β reaching 91.44° at 10 K. In the work presented here, powder neutron diffraction is used to explore the monoclinicity at 8 K 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, ( ac cos β) 2, suggests that the distortion vanishes at x=0.13. A reanalysis of single-crystal diffraction data on the magnetically ordered side of the phase diagram, x>0.1, indicates that long-range order disappears at exactly the same critical concentration. 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.
Published Version
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