The response of a triangular antiferromagnet to anisotropic lattice distortion

The ground state of Heisenberg spins interacting antiferromagnetically on a triangular lattice is 120$^{\circ}$ antiferromagnetic order. We probe the effects of anisotropic lattice distortion on this phase using the material PdCrO$_2$, which has highly-conducting Pd sheets that alternate with Mott-insulating CrO$_2$ layers. The Cr spins order into a 120$^{\circ}$ phase at T$_N$ = 39 K. The conductivity of the Pd sheets can be measured to probe magnetic scattering across the transition. In the unstrained lattice, the resistivity has a sharp first-order-like step at T$_N$. This step persists up to uniaxial compression by $\sim 0.3\%$, then splits into two much broader transitions. This feature suggests a rigidity of the 120$^{\circ}$ phase at T $\sim T_N$ against small perturbations, which we discuss in terms of magnetoelastic coupling and fluctuation effects.