Elastic Constants and Acoustic Absorption Coefficients in MnO, CoO, and NiO Single Crystals at Room Temperature

Abstract

Sound velocity and absorption coefficient have been measured for three antiferromagnetic crystals—MnO, CoO, and NiO—at 23±1°C by the pulse superposition method and the pulse-echo method, respectively. Elastic constants have been calculated from the velocity data: c11 = 22.20, c12 = 10.99, c44 = 7.83 for MnO: c11 = 25.56, c12 = 14.36, c44 = 8.03 for CoO; and c11 = 27.0, c12 = 12.5, c44 = 10.5 for NiO (in 1011 dyn/cm2). The absorption coefficients are found to be proportional to square of frequency between about 60 and 500 MHz for MnO and CoO and between 10 and 50 MHz for NiO. The absorption of the shear wave is of comparable order to that of the longitudinal wave in the paramagnetic phase (MnO and CoO), and this fact suggests that single-ion magnetostrictive interaction rather than the volume magnetostrictive interaction is a dominant cause for the acoustic attenuation in these materials.