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Ultrasound Investigations of Orbital Quadrupolar Ordering in UPd3

N. Lingg, D. Maurer, V. Müller, K. A. McEwen

cond-mat.str-elarXiv:cond-mat/9908271

Abstract

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 specified.

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