Microscopic identity of the 10 meV excitation

Determine whether the approximately 10 meV magnetic excitation in DyOCl is a renormalized crystal-field excitation, a collective multipolar excitation, or a mixed magnetoelastic mode, and thereby establish its relationship to the thermodynamic anomaly at T_Q.

Background

Inelastic neutron scattering identifies a weakly dispersive mode near 10 meV in DyOCl with momentum dependence consistent with magnetic scattering. The mode broadens, softens, and loses resolution as the temperature approaches T_Q, linking its evolution to the higher-temperature anomaly rather than directly to the onset of static dipolar order at T_N.

Restricted static single-ion models containing dipolar or phenomenological quadrupolar fields cannot simultaneously reproduce the 10 meV feature and the 24–30 meV crystal-field excitations. The authors therefore leave unresolved whether the mode originates from renormalized single-ion levels, collective multipolar dynamics, or magnetoelastic coupling; polarized single-crystal inelastic neutron scattering and complementary lattice-sensitive probes are proposed as tests.