Elastic properties of Tb0.3Dy0.7Fe2 measured ultrasonically

Abstract

Ultrasonic velocity and absorption measurements have been made as a function of magnetic field in both single crystal and polycrystalline Tb0.3Dy0.7Fe2. This highly magnetostrictive material exhibits a huge ΔE effect as previously reported at sonic frequencies. [A. E. Clark and H. T. Savage, IEEE Trans. Sonics Ultrason. SU-22, 50–52 (1975).] ΔE is the difference in Young's modulus between the magnetized and the unmagnetized state E0. In a polycrystalline bar sample, we measured an increased extensional velocity as a function of applied field (to 6 KOe) which corresponded to a ΔE/E0 of nearly 100%. A peak in the low field relative attenuation, with a corresponding velocity minimum, has been observed. These measurements were made at room temperature over a frequency range of 0.05 to 0.25 MHz. Bulk shear and longitudinal velocity measurements have been made from 1 to 21 MHz in both single crystal and polycrystalline samples. Measurements of sound propagation along [110] show that the crystal is elastically isotropic. Taking the density to be 9.25 g/cm2, at 12 MHz we calculate C11 = 11.7, 12(C11 − C12) = 3.84, and C44 = 3.84(× 1011 dyn/cm2). [Work supported by ONR.]