Elastic constants of single crystal erbium

The single crystal elastic constants of erbium were determined by means of an ultrasonic pulse technique as a function of temperature (10-300K) and magnetic field strength (0-3.9 T) along the c axis. Pronounced anomalies for most of the constants were observed in zero field at the Neel (85K) and Curie (20K) temperatures, as well as at 53K, at which temperature magnetic ordering in the basal plane sets in. Application of a field tries to restore the values of C 11 and 1 / 2 (C 11 -C 12 ) to what one would expect for a 'non-magnetic' crystal, while in the case of C 33 and C 44 it leads to very large softenings of the constants near 53K. A qualitative comparison is made with the predictions of Southern and Goodings (1973) which is based on single-ion anisotropic magnetoelastic terms.