Temperature-dependent Raman and IR studies of multiferroic MnWO4 doped with Ni2+ ions

Temperature-dependent Raman and IR studies of MnWO4 crystal doped with Ni2+ ions were performed in the 4.2–300 K range. These studies were complemented by magnetization and specific heat measurements in the 2–100 K range, which revealed that MnWO4 crystal doped with Ni2+ ions exhibits two phase transitions at 13.9 and 12.5 K. Temperature evolution of Raman wavenumbers and linewidths revealed anomalous behaviour at low temperatures. These anomalies have been attributed to spin–phonon coupling, which appear due to onset of antiferromagnetic spin ordering. The observed anomalies extend above TN = 13.9 K. This behaviour is consistent with the fact that MnWO4 is a moderately magnetically frustrated material.

Policrystalline Raman and IR spectra of Mn0.927Ni0.073WO4.Figure optionsDownload as PowerPoint slideHighlights
► New multiferroic compound Mn0.927Ni0.073WO4 was synthesized.
► Low temperature anomalous behaviour of phonons was found.
► Possible origin of this effect was discussed and attributed mainly to spin–phonon coupling.
► Phase transition occurring for MnWO4 at 7.5 K is no longer observed in Mn0.927Ni0.073WO4 crystal.