ULTRASONIC ATTENUATION AT MAGNETIC PHASE TRANSITIONS

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. © 1969 The American Institute of Physics.