  The CeT2Al10 family of orthorhombic compounds exhibits a very peculiar
evolution from a Kondo-insulator (T: Fe) to an unconventional long-range
magnetic order (T: Ru, Os). Inelastic neutron scattering experiments performed
on single-crystal CeFe2Al10 reveal that this material develops a spin-gap in
its magnetic spectral response below ~ 50 K, with a magnetic excitation
dispersing from $E = 10.2 \pm 0.5$ meV at the Y zone-boundary point [q =
(0,1,0)] to $\approx 12$ meV at the top of the branch. The excitation shows a
pronounced polarization of the magnetic fluctuations along a, the easy
anisotropy axis. Its behavior is contrasted with that of the (magnonlike) modes
previously reported for CeRu2Al10, which have transverse character and exist
only in the antiferromagnetic state. The present observation is ascribed to a
"magnetic exciton" mechanism invoked to explain a similar magnetic response
previously discovered in YbB12.
