  Elastic and inelastic neutron scattering measurements have been performed on
powder and single-crystal samples of orthorhombic CeRu2Al10. The order forming
below T0 = 27 K was identified as a long-range antiferromagnetic state with the
wave vector k = (1,0,0). The magnetic spectral response in the ordered phase,
measured on powder, is characterized by a spin gap and a pronounced peak at 8
meV, whose Q dependence suggests a magnetic origin. Both features are
suppressed when temperature is raised to T0, and a conventional relaxational
behavior is observed at 40 K. This peculiar spin dynamics is discussed in
connection with recent magnetization results for the same compound.

Strongly Correlated Electrons