An inelastic neutron scattering study of the spin dynamics of Yb1-xLuxAl3

We present the results of a systematic inelastic neutron scattering study of the spin dynamics of the mixed valent compound YbAl3 doped with nonmagnetic lutetium. The aim of the investigation is to clarify the origin of the unusual gap-like magnetic response observed in YbAl3, which can be modeled by two inelastic peaks: a narrow peak at 34 meV with HWHM, r = 6.4 ± 0.8 meV and a broad peak at 44 meV with Λ = 30 ± 1 meV. Lutetium substitution leads to a substantial increase in the linewidth (Λ = 9 ± 1 meV at x = 0.1) and a decrease in the intensity (down by 60% at x = 0.1) of the narrow component, with a negligible effect on the broad inelastic peak. This trend is confirmed with higher doping resulting in the complete suppression of the narrow peak at x ≥ 0.35. The results indicate that the narrow component arises from coherent excitation processes within the hybridized 4f-band, which are destroyed by disorder, while the broad component is not so sensitive to the loss of coherence