Magnetic and Structural Quantum Phase Transitions in CeCu6−xAux are Independent

Abstract

The heavy-fermion compound CeCu_{6-x}Au_{x} has become a model system for unconventional magnetic quantum criticality. For small Au concentrations 0≤x<0.16, the compound undergoes a structural transition from orthorhombic to monoclinic crystal symmetry at a temperature T_{s} with T_{s}→0 for x≈0.15. Antiferromagnetic order sets in close to x≈0.1. To shed light on the interplay between quantum-critical magnetic and structural fluctuations we performed neutron-scattering and thermodynamic measurements on samples with 0≤x≤0.3. The resulting phase diagram shows that the antiferromagnetic and monoclinic phase coexist in a tiny Au concentration range between x≈0.1 and 0.15. The application of hydrostatic and chemical pressure allows us to clearly separate the transitions from each other and to explore a possible effect of the structural transition on the magnetic quantum-critical behavior. Our measurements demonstrate that at low temperatures the unconventional quantum criticality exclusively arises from magnetic fluctuations and is not affected by the monoclinic distortion.

Quantitative investigation of the 4f occupation in the quasikagome Kondo lattice CeRh1−xPdxSn

“…This is a great surprise because in cerium compounds pressure tends to suppress magnetic order (see, e.g., Refs. [27,28] and references therein). The formation of the magnetic ground state upon application of uniaxial pressure in the ab plane has, therefore, been interpreted in terms of a stress induced reduction of geometrical frustration in the hexagonal plane.…”

Ferroelectric order versus metallicity in Sr1−xCaxTiO3−δ ( x<

“…In the vicinity of a quantum critical point Γ exhibits a sign change 37 , which results from a sign change of α, because c p is always positive 38 . Experimentally, such sign changes of α are observed in diverse materials where the control parameter is either a magnetic field [39][40][41][42][43][44][45] , a chemical or hydrostatic pressure 46 , or the charge-carrier concentration 47 .…”

Antiferromagnetic Correlations in Strongly Valence Fluctuating CeIrSn

“…Since the expansion coefficient measures the pressure derivative of entropy, the entropy accumulation near a quantum critical point (QCP) results in a sign change of thermal expansion [15]. In particular, a characteristically negative thermal expansion is observed when the ground state is tuned through a magnetic QCP to an AF ordered state [16][17][18].…”

“…The negative in-plane thermal expansion without discontinuity observed in CeIrSn may thus indicate a short-range order. We recall that a negative thermal expansion manifests itself in Ce-based compounds such as CeCu 6−x Au x and CeRhIn 5−x Sn x when crossing the magnetic QCPs from a paramagnetic to an AF ordered state [16,17].…”