Raman scattering at the magnetic phase transition in a LiNiPO4 single crystal
B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine 47 Nauky Ave., Kharkiv 61103, Ukraine
Received January 31, 2020, published online April 24, 2020
The temperature evolution of Raman scattering in a LiNiPO4 single crystal was studied near the phase transition to a magnetically ordered in the range of 2–25 K. For the first time, in the Raman spectra, the magnetic contribution was divided into single-magnon and two-magnon excitations revealed at 2 K. The energies of the detected single-magnon excitations are in good agreement with the data previously obtained from transmis-sion IR spectra. The shape of the two-magnon scattering band is in good accordance with published data for the two-magnon density of states. We observed a red shift of a number of phonon lines upon transition to a magnetically ordered state. This fact is explained by the significant magnon-phonon interaction. We have revealed the change in the intensities of Raman spectra below TN depending on the polarization of the excited light. We suppose that this effect is associated with a shift of the Ni2+ absorption bands in the region of the 532 nm excitation line as a result of magnetic ordering. This indicates a significant interaction of the electronic and magnetic subsystems in the studied crystal.
Key words: Raman spectroscopy, magnetic phase transition, single-magnon scattering, two-magnon scattering, LiNiPO4.