Low-Temperature Structural Phase Transition in Monoclinic RbDy(WO$\text{}_{4}$)$\text{}_{2}$ Crystal

The ESR spectrum of Dy$\text{}^{3+}$ ion in the low-symmetry RbDy(WO$\text{}_{4}$)$\text{}_{2}$ crystal has been studied in the temperature region of T=4.2 ÷ 30K. The ESR linewidth was found to increase from 130 mT up to the maximum value of 190 mT at T=9K and then to decrease down to 150 mT at 4.2K. The components of the g-tensor change considerably without change of their spatial orientation in the temperature range from 12K to 7 K: g$\text{}_{z}$=2.5, g$\text{}_{x}$≈0, g$\text{}_{y}$=1.41 at T>12 K; g$\text{}_{z}$=1.53, g$\text{}_{x}$≈0, g$\text{}_{y}$=1.2 at T<7K. The observed λ-shaped behaviour of absorption linewidth and the decrease in the g-factor are assumed to be due to the low-temperature structural phase transition (T$\text{}_{SPT}$≈9 K). The width of the transition area is of about 5K. It is suggested that the symmetry of high- and low-temperature phases is identical.