Elastic anomalies associated with structural and magnetic phase transitions in single crystal hexagonal YMnO3

Resonant ultrasound spectroscopy has been used to measure the elastic and anelastic behaviour through known structural and magnetic phase transitions in single crystal hexagonal YMnO3. Anomalous elastic behaviour is observed at the high temperature structural transition at similar to 1260 K, with a discontinuity in the elastic constants and nonlinear recovery below T-c, consistent with lambda eQ(s)(2) coupling. There is no change in dissipation associated with this high temperature transition, and no evidence in the elastic or anelastic behaviour for any secondary transition at similar to 920 K, thus supporting the thesis of a single high temperature transformation. Elastic stiffening is observed on cooling through T-N, in accordance with previous studies, and the excess elastic constant appears to scale with the square of the magnetic order parameter. The strains incurred at T-N are a factor of similar to 20 smaller than those at the structural transition, implying very weak lambda eQ(m)(2) coupling and a dominant contribution to the variation in the elastic constants from lambda e(2)Q(m)(2). The increased acoustic dissipation above T-N is consistent with an order-disorder process.