Magnetic effects on the elastic constants of praseodymium

Ultrasonic studies of the elastic constant, c66, of DHCP Pr are reported. Using CdS thin-film transducers c66 was measured as a function of temperature and as a function of an applied magnetic field at 4.2 K. c66 is found to be strongly affected by a field applied in the basal plane, whereas the application of a field along the c-axis has almost no effect. this behaviour reflects the anisotropy of the magnetic susceptibility of the hexagonal ions, indicating that they dominate the magnetic effects on c66. Neglecting magnetic contributions from the cubic ions, the observed behaviour of c66 is in agreement with the calculations based on the magnetic Hamiltonian for the hexagonal ions which has been deduced from the field dependence of the magnetic excitations. (author)