One-dimensional magnetic fluctuations in the spin-2 triangular lattice α-NaMnO2

The S=2 anisotropic triangular lattice α-NaMnO2 is studied by neutron inelastic scattering. Antiferromagnetic order occurs at Tâ?¤45K with opening of a spin gap. The spectral weight of the magnetic dynamics above the gap (Î?7.5meV) has been analyzed by the single-mode approximation. Excellent agreement with the experiment is achieved when a dominant exchange interaction (|J|/kB73K), along the monoclinic b axis and a sizable easy-axis magnetic anisotropy (|D|/kB3K) are considered. Despite earlier suggestions for two-dimensional spin interactions, the dynamics illustrate strongly coupled antiferromagnetic S=2 chains and cancellation of the interchain exchange due to the lattice topology. α-NaMnO2 therefore represents a model system where the geometric frustration is resolved through the lowering of the dimensionality of the spin interactions. © 2009 The American Physical Society