Ultrasound studies of single crystal thulium in an applied magnetic field

The paper reports the first measurements of the single crystal elastic constants of the heavy rare earth metal thulium as a function of temperature and magnetic field. The constants were obtained from ultrasonic velocity measurements over a temperature range of 4.2–296 K and in applied magnetic fields of up to 5 T. The elastic constants; C 11 , C 33 , C 44 and C 66 =(C 11 –C 12 )/2 were determined from the ultrasonic velocities. Anomalies in the elastic constants were observed at 58 K from the c -axis propagated shear wave measurements and at 55 K from the c -axis propagated longitudinal wave measurements. Significant softening of the elastic constants C 33 and C 44 was observed close to T N . Application of a magnetic field (>2 T) along the c -axis direction induced further softening of the material. Electromagnetic acoustic transducers (EMATs) were also employed in addition to conventional piezoelectric quartz transducers. A marked increase in the EMATs acoustic coupling efficiency (generation and detection efficiency) occurred close to T N .