Magnetic interactions in PdCrO2 and their effects on its magnetic structure

We report a neutron scattering study of the metallic triangular lattice antiferromagnet PdCrO2. Powder neutron diffraction measurements confirm that the crystalline space group symmetry remains R (3) over barm below T-N. This implies that magnetic interactions consistent with the crystal symmetry do not stabilize the noncoplanar magnetic structure, which was one of two structures previously proposed on the basis of single crystal neutron diffraction measurements. Inelastic neutron scattering measurements find two gaps at low energies, which can be explained as arising from a dipolar-type exchange interaction. This symmetric anisotropic interaction also stabilizes a magnetic structure very similar to the coplanar magnetic structure, which was also suggested by the single crystal diffraction study. The higher-energy magnon dispersion can be modelled by linear spin-wave theorywith exchange interactions up to sixth nearest neighbors, but discrepancies remain which hint at additional effects unexplained by the linear theory.