ULTRASONIC BEHAVIOR NEAR SPIN-FLOP TRANSITIONS OF HEMATITE

Ultrasonic propagation in natural single crystals of hematite (-Fe2O3) was studied in magnetic fields up to 200 kG at various temperatures between 4.2 and 300°K. Anomalies in the ultrasonic attenuation were observed near: (1) the spin-flop transition at Hc (in a field parallel to the trigonal axis), (2) the spin-flop transition at Hc (in a field normal to the trigonal axis), and (3) the Morin transition. Anomalies in the velocity of some acoustical modes of propagation were also observed at Hc. The temperature variation of Hc and Hc was studied in one of the hematite crystals which had a low impurity content. At 77°K, Hc=68.20.7 kG and Hc=160.82 kG. The Morin transition in this crystal occurs at TM=(260.60.5)°K. The ultrasonic data can be accounted for by considering the motion of domain walls under the action of an oscillating elastic stress. Other explanations are also considered. The data for Hc and Hc are compared with the results of other workers. © 1969 The American Physical Society.