Observation of spontaneous ferriquadrupolar order in KDy(MoO4)2

Using Raman and infrared spectroscopies, spontaneous ferriquadrupolar ordering has been observed in the rare-earth-based system KDy(MoO4)(2). Ordered quadrupoles in the electron subsystem attend nonequivalent distortions of rare-earth ions in the ordered phase. A mean-field theory explaining the onset of such a type of ordering has been constructed.