Unusual magnetic response of intermediate-valent YbPd andYb3Pd4as studied by inelastic neutron scattering

We report on some novel features of the magnetic response of intermediate-valence Yb compounds as seen by inelastic magnetic neutron scattering. We firstly confirm the existence of magnetic phase transitions in intermediate-valent YbPd and ${\mathrm{Yb}}_3$ ${\mathrm{Pd}}_4$ by observing magnon excitations below and additional Gaussian quasielastic lines above the ordering temperatures. We then show that it is the very small magnetic fluctuation rate at helium temperatures which enables these systems to order magnetically. On the other hand, the very large quasielastic linewidth observed at higher temperatures ensures that YbPd is indeed in an intermediate-valent state. We also find for the first time two different quasielastic linewidths in these systems, which differ strongly in their temperature dependence. Distinct inelastic excitations can be interpreted in terms of crystal-field theory. The crystal-field ground states have nonvanishing quadrupole moments, whose interactions enhance the magnetic ordering temperatures in both systems.