Anomalous spin-waves and the commensurate-incommensurate magnetic phase transition in LiNiPO4

TL;DR

This study investigates the spin-wave spectra of LiNiPO4, revealing anomalous modes and the mechanisms behind the commensurate-incommensurate magnetic phase transition using neutron scattering and a linear spin-wave model.

Contribution

It provides a detailed analysis of spin-wave spectra in LiNiPO4 and explains the incommensurate phase transition through a model incorporating exchange interactions and anisotropies.

Findings

Anomalous low-energy mode observed at the incommensurate phase vector.

Strong next-nearest-neighbor AF coupling causes incommensurate structure.

Linear spin-wave model successfully explains observed dispersions.

Abstract

Detailed spin-wave spectra of magneto-electric LiNiPO4 have been measured by neutron scattering at low temperatures in the commensurate (C) antiferromagnetic (AF) phase with ordering temperature 20.8 K. An anomalous low-energy mode is observed at the modulation vector of the incommensurate (IC) AF phase appearing above the 20.8 K. A linear spin-wave model based on Heisenberg exchange couplings and single ion anisotropies accounts for all the observed spin-wave dispersions and intensities. Along the b axis an unusually strong next-nearest-neighbor AF coupling competes with the dominant nearest-neighbor AF exchange interaction and causes the IC structure.