The temperature dependence of the elastic constants of MnO

We have measured the temperature dependence of the elastic constants of a monodomain single crystal of MnO, obtained by applying a unixial stress, from 4.2 to 300 K. Measurements were made by standard ultrasonic techniques and the acoustic waves were generated and detected by CdS transducers. Problems associated with the coupling between transducer and sample encountered by previous workers were therefore overcome. For propagation down the [111] direction, only the slow shear mode [$\text{1}\text{2}$(c₁₁?c₁₂)] was observable below the Néel temperature (T_N. The fast shear and longitudinal modes were heavily attenuated. Complex behaviour in the region of T_N and a further anomaly at 42 K were observed.