Magnetic excitations in the ordered phases of praseodymium hexaboride

We have made the first inelastic neutron scattering measurements on single crystal PrB(6), studying the magnetic excitations in the ordered phases. The lowest energy mode has a minimum energy of approximate to 1.0 meV at the magnetic zone centre, with a significant dispersion along the [001] direction, but very little dispersion along [110]. Interactions out to fourth nearest neighbours are required to explain the [001] dispersion. Measurements of the temperature dependence of the excitations show a strong softening and broadening of the lowest energy mode at the magnetic zone centre between 2 K (commensurate phase) and 5 K (incommensurate phase).