1 9 A ug 1 99 9 Ultrasound Investigations of Orbital Quadrupolar Ordering in UPd 3
نویسنده
چکیده
For a high-quality single crystal of UPd3 we present the relevant elastic constants and ultrasonic attenuation data. In addition to the magnetic phase transition at T2 = 4.4±0.1K and the quadrupolar transition at T1 ∼ 6.8K, we find orbital ordering at T0 = 7.6±0.1K concomitant with a symmetry change from hexagonal to orthorhombic. A striking feature is the splitting of the phase transition at T1 into a second-order transition at T+1 = 6.9±0.05K and a first-order transition at T−1 = 6.7 ± 0.05K. For the four phase transitions, the quadrupolar order parameters and the respective symmetry changes are
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