  The dynamic magnetic properties of the Kondo-insulator state in CeFe2Al10
(spin gap, resonance mode) have been investigated using polarized neutrons on a
single crystal of pure CeFe2Al10. The results indicate that the magnetic
excitations are polarized mainly along the orthorhombic a axis and their
dispersion along the orthorhombic c direction could be determined.
Polycrystalline samples of Nd- and Rh-doped CeFe2Al0 were also studied by the
time-of-flight technique, with the aim of finding out how the low-energy
magnetic excitation spectra change upon isoelectronic substitution of the
rare-earth (Nd) on the magnetic Ce site or electron doping (Rh) on the
transition-element Fe sublattice. The introduction of magnetic Nd impurities
strongly modifies the spin gap in the Ce dynamic magnetic response and causes
the appearance of a quasielastic signal. The crystal-field excitations of Nd,
studied in both LaFe2Al10 and CeFe2Al10, also reveal a significant influence of
f-electron hybridization (largest in the case of Ce) on the crystal-field
potential. As a function of the Rh concentration, a gradual change is observed
from a Kondo-insulator to a metallic Kondo-lattice response, likely reflecting
the decrease in the hybridization energy.

Strongly Correlated Electrons