Inelastic neutron scattering study of the spin dynamics of Yb1-xLuxAl3

We present the results of a systematic inelastic neutron scattering study o f the spin dynamics of the mixed valent compound YbAl3 doped with nonmagnet ic lutetium. The aim of the investigation is to clarify the origin of the u nusual gap-like magnetic response observed in YbAl3, which can be modeled b y two inelastic peaks: a narrow peak at 34 meV with half width at half maxi mum, Gamma = 6.4 +/- 0.8 meV and a broad peak at 44 meV with Gamma = 30+/- 1 meV. Lutetium substitution leads to a substantial increase in the linewid th (Gamma = 9 +/- 1 meV at x = 0.1) and a decrease in the intensity (down b y 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 greater than or equal t o 0.35. The results indicate that the narrow component arises from coherent excitation processes within the hybridized 4f band. (C) 1999 American Inst itute of Physics. [S0021-8979(99)54108-X].