Observation of the novel type of ordering: Spontaneous ferriquadrupolar order

Using Raman and infrared spectroscopies the spontaneous ferriquadrupolar ordering has been observed in the rare-earth-based system KDy(MoO${}_4$)${}_2$. 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.