Onset of antiferromagnetism in heavy fermion metals

Abstract

There are two views of antiferromagnets. The first proceeds from atomic physics, which predicts that atoms with unpaired electrons develop magnetic moments. In a solid, the coupling between moments on nearby ions then yields antiferromagnetic order at low temperatures. The second, based on the physics of electron fluids or 'Fermi liquids', states that Coulomb interactions can drive the fluid to adopt a more stable configuration by developing a spin density wave. It is presently unknown which view is appropriate at a `quantum critical point', where the antiferromagnetic transition temperature vanishes. Here we describe an atomically local contribution to the magnetic correlations which develops in the metal CeCu$_{6-x}$Au$_{x}$ at the critical gold concentration ($x_c=0.1$) where the magnetic ordering temperature is tuned to zero. This contribution implies that a Fermi-liquid destroying spin-localizing transition, unanticipated for the spin density wave description, coincides with the antiferromagnetic quantum critical point.