Elastic constants of U(Ru_1-xRh_x)₂Si ₂

Ultrasonic measurements on Rh-substitution system U(Ru_1-xRh _x)₂Si₂ (x = 0, 0.02 and 0.07) were performed in order to investigate lattice properties for low temperature phase transitions of 'hidden order' (HO) phase and antiferromagnetc (AFM) phase. Elastic constant C₁₁ vs. T of the x = 0.02 and 0.07 samples exhibit a depression below 80 K, which is similar to a softening in the non-doped sample which had already been reported. The C₁₁ of x = 0.02 exhibits a step-like anomaly at 14.0 K and an additional softening of 3.2% with minimum at 6.7 K, which correspond to HO and AFM transitions, respectively. The C₁₁ in x = 0.07 sample only exhibits a shoulder-like anomaly at around 17 K and continue to depress down to 4.2 K.