  In the triangular layered magnet PdCrO2 the intralayer magnetic interactions
are strong, however the lattice structure frustrates interlayer interactions.
In spite of this, long-range, 120$^\circ$ antiferromagnetic order condenses at
$T_N = 38$~K. We show here through neutron scattering measurements under
in-plane uniaxial stress and in-plane magnetic field that this occurs through a
spontaneous lifting of the three-fold rotational symmetry of the nonmagnetic
lattice, which relieves the interlayer frustration. We also show through
resistivity measurements that uniaxial stress can suppress thermal magnetic
disorder within the antiferromagnetic phase.
