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 similar to 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 T-1(-1) around T approximate to 25 K. This novel finding is discussed within the context of excitations in the triangular Heisenberg antiferromagnets.