Low-temperature structural phase transition in monoclinic RbDy(WO4)2 crystal

The ESR spectrum of Dy3+ ion in the low-symmetry RbDy(WO4)(2) crystal has been studied in the temperature region of T = 4.2 divided by 30 K. The ESR linewidth was found to increase from 130 mT up to the maximum value of 190 mT at T = 9 It and then to decrease down to 150 mT at 4.2 K. The components of the g-tensor change considerably without change of their spatial orientation in the temperature range from 12 K to 7 K: g(z) = 2.5, g(x) approximate to 0, g(y) = 1.41 at T > 12 K; g(z) = 1.53, g(x) approximate to 0, g(y) = 1.2 at T < 7 K. The observed X-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-SPT approximate to 9 K) The width of the transition area is of about 5 K. It is suggested that the symmetry of high- and low-temperature phases is identical.