Ultrasound studies of single crystal thulium in an applied magnetic field

The paper reports the first measurements of the single crystal elastic cons tants of the heavy rare earth metal thulium as a function of temperature an d magnetic field. The constants were obtained from ultrasonic velocity meas urements over a temperature range of 4.2-296 K and in applied magnetic fiel ds 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 ela stic 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 measu rements. Significant softening of the elastic constants C-33 and C-44 was o bserved close to T-N. Application of a magnetic field (> 2T) along the c-ax is direction induced further softening of the material. Electromagnetic aco ustic transducers (EMATs) were also employed in addition to conventional pi ezoelectric quartz transducers. A marked increase in the EMATs acoustic cou pling efficiency (generation and detection efficiency) occurred close to T- N. (C) 2001 Elsevier Science B.V. All rights reserved.