  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.
