Magnetic Ordering in Single-Crystal Praseodymium Induced by Uniaxial Stress

Neutron inelastic scattering techniques have been used to examine the dispersion relations for magnetic excitons propagating on the hexagonal sites of double-hcp Pr when uniaxial stress is applied along the [12̄10] direction. The mode of lowest energy (longitudinal optic) along ΓM was found to exhibit a clear soft-mode behavior with increasing stress. Elastic satellite reflections corresponding to long-range magnetic ordering in a longitudinally modulated structure were observed: at 800 bars the N\'eel temperature is 7.5 K.