Neutron scattering and scaling behavior in URu2Zn20 and YbFe2Zn20

The dynamic susceptibility {chi}*({Delta}E), measured by inelastic neutron-scattering measurements, shows a broad peak centered at E{sub max} = 15 meV for the cubic actinide compound URu{sub 2}Zn{sub 20} and 7 meV at zone center and at the (1/2, 1/2, 1/2) zone boundary for the rare-earth counterpart compound YbFe{sub 2}Zn{sub 20}. For URu{sub 2}Zn{sub 20}, the low-temperature susceptibility and magnetic specific-heat coefficient {gamma} = C{sub mag}/T take the values {chi} = 0.011 emu/mole and {gamma} = 190 mJ/mole K{sup 2} at T = 2 K. These values are roughly three times smaller, and E{sub max} is three times larger, than recently reported for the related compound UCo{sub 2}Zn{sub 20}, so that {chi} and {gamma} scale inversely with the characteristic energy for spin fluctuations, T{sub sf} = E{sub max}/k{sub B}. While {chi}(T), C{sub mag}(T), and E{sub max} of the 4f compound YbFe{sub 2}Zn{sub 20} are very well described by the Kondo impurity model, we show that the model works poorly for URu{sub 2}Zn{sub 20} and UCo{sub 2}Zn{sub 20}, suggesting that the scaling behavior of the actinide compounds arises from spin fluctuations of itinerant 5f electrons.