Inelastic neutron scattering from PrFe$_4$P$_{12}$ at low temperatures and under high magnetic fields
J.-G. Park, D. T. Adroja, K. A. McEwen, M. Kohgi, and K. Iwasa

PrFe$_4$P$_{12}$ exhibits a unique transition at 6.5 K with an order parameter, whose nature is still controversial. In order to elucidate the origin of the transition, we have carried out inelastic neutron scattering experiments at a range of temperatures and magnetic fields. Our data reveals a new type of low-lying excitations centered at 1.5 and 3.5 meV in the ordered phase with an unusual Q-dependence. With increasing field or temperature, the well-defined excitations develop into a quasi-elastic response while the ordered phase becomes a paramagnetic state with a very large characteristic energy scale of $\Gamma$ $\simeq$ 0.8 meV, consistent with a large Sommerfield coefficient $\gamma$ = 1.4 J/mol-K$^2$.

© 2008 The American Physical Society.