Spin dynamics of frustrated easy-axis triangular antiferromagnet 2H-AgNiO2 explored by inelastic neutron scattering

TL;DR

This study investigates the spin dynamics in the frustrated triangular antiferromagnet 2H-AgNiO2 using inelastic neutron scattering, revealing dispersive magnetic excitations influenced by anisotropy and frustration, with theoretical analysis supporting experimental observations.

Contribution

The paper provides a detailed experimental and theoretical analysis of spin-wave excitations in 2H-AgNiO2, highlighting the effects of easy-axis anisotropy and frustration on the dispersion relations.

Findings

Broad magnetic excitation band up to 7.5 meV

Anomalous dispersion minima at soft points due to frustration

Quantum corrections reduced by easy-axis anisotropy

Abstract

We report inelastic neutron scattering measurements of the spin dynamics in the layered hexagonal magnet 2H-AgNiO2 which has stacked triangular layers of antiferromagnetically-coupled Ni2+ spins (S=1) ordered in a collinear alternating stripe pattern. We observe a broad band of magnetic excitations above a small gap of 1.8 meV and extending up to 7.5 meV, indicating strongly dispersive excitations. The measured dispersions of the boundaries of the powder-averaged spectrum can be quantitatively explained by a linear spin-wave dispersion for triangular layers with antiferromagnetic nearest- and weak next-nearest neighbor couplings, a strong easy-axis anisotropy and additional weak inter-layer couplings. The resulting dispersion relation has global minima not at magnetic Bragg wavevectors but at symmetry-related soft points and we attribute this anomalous feature to the strong competition between the easy-axis anisotropy and the frustrated antiferromagnetic couplings. We have also calculated the quantum corrections to the dispersion relation to order 1/S in spin-wave theory by extending the work of Chubukov and Jolicoeur [Phys. Rev. B v46, 11137 (1992)] and find that the presence of easy-axis anisotropy significantly reduces the quantum renormalizations predicted for the isotropic model.