Ultrasonic Behavior near the Spin-Flop Transition ofCr2O3

The attenuation of longitudinal and shear ultrasonic waves exhibits a peak at the spin-flop transition of ${\mathrm{Cr}}_2$ ${\mathrm{O}}_3$. This peak is attributed to the presence of antiferromagnetic domains near the transition. The attenuation peak for longitudinal waves is accompanied by a dip in the phase velocity. The temperature variation of the spin-flop-transition field $H_{\mathrm{sf}}$ was measured from 4.2 to 305°K and is in very good agreement with earlier differential magnetization data obtained by Foner and Hou. At 4.2°K, $H_{\mathrm{sf}}=60.3\mathrm{}\pm 1.0$ kG, whereas at 305°K, $H_{\mathrm{sf}}=121.2\mathrm{}\pm 1.5$ kG.