AN ULTRASONIC STUDY OF ANTIFERROMAGNETIC DYSPROSIUM

Elastic constant C-33 and its associated ultrasonic attenuation alpha( 33) have been measured for the single crystal of Dy using 50 MHz longi tudinal sound waves along the c-axis, between 77-300 K. On the tempera ture dependence of C-33 in the helical state (T-c<T<T-N) Were observed the only anomaly at 114 and 156 K while on the temperature variation of alpha(33) were revealed the peaks at 116, 132, 145 and 156 It. The anomalies have been interpreted in term angles with are commensurate w ith the basal plane hexagonal crystal structure.