Anomalous spin waves and the commensurate-incommensurate magnetic phase transition in LiNiPO4
Detailed spin-wave spectra of magnetoelectric LiNiPO4 have been measured by neutron scattering at low temperatures in the commensurate (C) antiferromagnetic (AF) phase below T-N=20.8 K. An anomalous shallow minimum is observed at the modulation vector of the incommensurate (IC) AF phase appearing above T-N. 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.
Keywords: antiferromagnetic materials; commensurate-incommensurate transformations; exchange interactions (electron); Heisenberg model; lithium compounds; magnetic anisotropy; magnetic transitions; magnetoelectric effects; neutron diffraction; nickel compounds; spin waves
Record created on 2010-02-08, modified on 2016-08-08