Absorption spectra behavior at the cooperative Jahn–Teller ordering in KDy(MoO4)2

Absorption spectra of KDy(MoO4)2 were studied in the wide temperature range, including the critical temperature of the pseudo-cooperative Jahn–Teller ordering (about 15 K). The spectra were also investigated in the low-temperature phase in external magnetic fields up to 7 T. These data were complemented with the temperature and magnetic fields dependences of birefringence. The possible existence of an intermediate phase (we supposed it as incommensurate) in the temperature range of 12–15 K is discussed. It is supposed that the considered model of the incommensurate phase may be applicable to other isostructural rare-earth rhombic molybdates.