Unconventional Dynamics in Triangular Heisenberg Antiferromagnet NaCrO₂

We report magnetization, specific heat, muon spin rotation, and Na NMR measurements on the S=3/2 rhombohedrally stacked Heisenberg antiferromagnet NaCrO₂. This compound appears to be a good candidate for the study of isotropic triangular Heisenberg antiferromagnets with very weak interlayer coupling. While specific heat and magnetization measurements indicate the onset of a transition in the range T_c∼40–50  K, both muon spin rotation and NMR reveal a fluctuating crossover regime extending well below T_c, with a peak of relaxation rate T₁^-1 around T≈25  K. This novel finding is discussed within the context of excitations in the triangular Heisenberg antiferromagnets.