Ultrasonic attenuation study of erbium in a magnetic field

The ultrasonic attenuation coefficient of longitudinal waves propagating along the c-axis of a single crystal of erbium was measured over a temperature range which covers the transition temperature from the paramagnetic to the sinusiodal phase T₆ = 83.8 K and the transition temperature from the sinusoidal to elliptical phase T_⊥ = 53.9 K. These measurements were performed as a function of temperature in the presence of constant magnetic fields and at constant temperatures as a function of applied magnetic fields. A magnetic field parallel to the c-axis shifted T₆ to lower temperatures and reduced the peak attenuation. A broad new maximum emerged on the high temperature side of the field-shifted T₆. Application of H perpendicular to the c-axis produced little change in either T₆ or T_⊥. A model introduced by Tachiki and Mackawa is used to discuss the results.