Heisenberg spins on an anisotropic triangular lattice: PdCrO2 under uniaxial stress

Abstract

When Heisenberg spins interact antiferromagnetically on a triangular lattice and nearest-neighbor interactions dominate, the ground state is 120° antiferromagnetism. In this work, we probe the response of this state to lifting the triangular symmetry, through investigation of the triangular antiferromagnet PdCrO _2 under uniaxial stress by neutron diffraction and resistivity measurements. The periodicity of the magnetic order is found to change rapidly with applied stress; the rate of change indicates that the magnetic anisotropy is roughly forty times the stress-induced bond length anisotropy. At low stress, the incommensuration period becomes extremely long, on the order of 1000 lattice spacings; no locking of the magnetism to commensurate periodicity is detected. Separately, the magnetic structure is found to undergo a first-order transition at a compressive stress of ∼0.4 GPa, at which the interlayer ordering switches from a double-to a single- q structure.

Keywords

• triangular lattice
• delafossite
• uniaxial stress
• antiferromagnetism
• neutron scattering