Raman scattering during a magnetic phase transition in a LiNiPO4 single crystal

Abstract

The temperature evolution of the LiNiPO4 single crystal Raman spectra in a region of 2–25 K, which includes a phase transition to a magnetically ordered state, is studied. For the first time, magnetic contribution in the Raman spectra was divided into single-magnon and two-magnon excitations at 2 K. The energies of the detected single-magnon excitations are in good agreement with the data obtained earlier from transmission spectra in the near-IR region. The shape of the two-magnon scattering band corresponds to the published data for the density of two-magnon states. A shift in some phonon lines was detected in the transition to a magnetically ordered state, which indicates a significant magnon-phonon interaction. A change in the scattering spectrum intensities below TN was observed, which depends on the polarization of the incident light. It is suggested that this effect is associated with a shift of the Ni2+-ion absorption bands during magnetic ordering in the region of the 532 nm excitation line. This indicates a significant interaction between the electronic and magnetic subsystems in the crystal under study.