Magnetic order on the spatially anisotropic triangular lattice of α-NaMnO2 is studied via neutron diffraction measurements. The transition into a commensurate, collinear antiferromagnetic ground state with k=(0.5,0.5,0) was found to occur below TN=22 K. Above this temperature, the transition is preceded by the formation of a coexisting, short-range ordered, incommensurate state below TIC=45 K whose two dimensional propagation vector evolves toward k=(0.5,0.5) as the temperature approaches TN. At high temperatures (T>TIC), quasielastic scattering reveals one-dimensional spin correlations along the nearest neighbor Mn-Mn "chain direction" of the MnO6 planes. Our data are consistent with the predictions of a mean field model of Ising-like spins on an anisotropic triangular lattice, as well as the predominantly one-dimensional Heisenberg spin Hamiltonian reported for this material.
@article{arxiv.1810.08637,
title = {Thermal evolution of quasi-1D spin correlations within the anisotropic triangular lattice of $\alpha$-NaMnO$_2$},
author = {Rebecca L. Dally and Robin Chisnell and Leland Harriger and Yaohua Liu and Jeffrey W. Lynn and Stephen D. Wilson},
journal= {arXiv preprint arXiv:1810.08637},
year = {2018}
}