Ultrasonic Attenuation at Magnetic Phase Transitions

Abstract

Recent quantitative measurements of frequency and temperature dependence of the ultrasonic attenuation in the vicinity of the magnetic phase transition for a number of materials (Gd, Tb, Dy, Ho, RbMnF₃, MnFr₂, Cr) enable us to compare these results critically with a number of recent theories. For each of these materials we know the spin‐phonon coupling mechanism and the coupling strength fairly well. The comparison shows that the anisotropic case (materials with a rather large uniaxial anisotropy) is better understood than the isotropic one. The only case where the spin‐phonon coupling is of the single ion magnetostrictive type, shear wave in Dy, the critical attenuation can be semiquantitatively accounted for by considering higher‐order spin components in the magnetoelastic Hamiltonian.