Using Raman and infrared spectroscopies the spontaneous ferriquadrupolar ordering has been observed in the rare-earth-based system KDy(MoO4)2. Ordered quadrupoles in the electron subsystem attend non-equivalent distortions of rare-earth ions in the ordered phase. The mean field theory explaining the onset of such a type of ordering has been constructed.
@article{arxiv.1810.00591,
title = {Observation of the novel type of ordering: Spontaneous ferriquadrupolar order},
author = {A. A. Zvyagin and K. Kutko and D. Kamenskyi and A. V. Peschanskii and S. Poperezhai and N. M. Nesterenko},
journal= {arXiv preprint arXiv:1810.00591},
year = {2018}
}