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

TL;DR

This study investigates the magnetic excitations in alpha-NaMnO2, revealing that it behaves as a system of strongly coupled one-dimensional antiferromagnetic chains with resolved geometric frustration, using neutron scattering data and theoretical modeling.

Contribution

It demonstrates that alpha-NaMnO2's magnetic dynamics are dominated by one-dimensional chains, resolving previous two-dimensional interaction assumptions through experimental and theoretical analysis.

Findings

Antiferromagnetic order at ~45 K with a spin gap of ~7.5 meV.

Dominant exchange interaction |J|/k_B ~ 73 K along the b-axis.

Strongly coupled S=2 antiferromagnetic chains with lattice topology-induced frustration.

Abstract

The S=2 anisotropic triangular lattice alpha-NaMnO2 is studied by neutron inelastic scattering. Antiferromagnetic order occurs at T ~ 45 K with opening of a spin gap. The spectral weight of the magnetic dynamics above the gap (Delta ~ 7.5 meV) has been analysed by the single-mode approximation. Excellent agreement with the experiment is achieved when a dominant exchange interaction (|J|/k_B ~ 73 K), along the monoclinic b-axis and a sizeable easy-axis magnetic anisotropy (|D|/k_B ~ 3 K) 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. alpha-NaMnO2 therefore represents a model system where the geometric frustration is resolved through the lowering of the dimensionality of the spin interactions.