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.
@article{arxiv.0902.2288,
title = {Anomalous spin-waves and the commensurate-incommensurate magnetic phase transition in LiNiPO4},
author = {T. B. S. Jensen and N. B. Christensen and M. Kenzelmann and H. M. Rønnow and C. Niedermayer and N. H. Andersen and K. Lefmann and M. Jiménez-Ruiz and F. Demmel and J. Li and J. L. Zarestky and D. Vaknin},
journal= {arXiv preprint arXiv:0902.2288},
year = {2009}
}
Comments
4 pages, 4 figures, accepted for publication in Phys. Rev. B