Tuning magnetic quantum phase transitions

In the canonical quantum-critical heavy-fermion system (HFS) CeCu6-xAux, a quantum critical point (QCP) can be obtained as a function of Au concentration at xc=0.1 or, for x>xc, by hydrostatic pressure p or magnetic field B. The different behavior of B and x tuning of the QCP inferred from specific heat and resistivity, is corroborated by inelastic neutron scattering probing critical fluctuations, indicating that the (B,x,p) phase diagram for T → 0 may exhibit several distinct phases. The Kondo temperature determined with UPS shows a sharp step at xc, suggestive of a loss of complete Kondo screening. Implications for QCP models for HFS are discussed. - Uniaxial stress imposed on epitaxially grown LaCoO3 films leads to the stabilization of a high-spin state, as opposed to bulk LaCoO3 which is non-magnetic with S=0 for T → 0. Unexpectedly, ferromagnetism with TC up to 80 K is observed in epitaxial films whose properties can be ''strain-tuned'' by choosing different substrates.