Effect of Nd and Rh substitution on the spin dynamics of the Kondo-insulator Ce Fe2Al10

The dynamic magnetic properties of the Kondo-insulator state in Ce Fe₂Al₁₀ (spin gap, resonance mode) have been investigated using polarized neutrons on a single crystal of pure Ce Fe₂Al₁₀ . 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 Ce Fe₂Al₁₀ 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 a rare-earth element (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 La Fe₂Al₁₀ and Ce Fe₂Al₁₀ , 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.