Kondo-lattice formation in cubic-phase ${\mathrm{YbCu}}_5$

The ${\mathrm{YbCu}}_5$ phase with $C15b$ structure has been prepared by a high-pressure technique, and its physical properties have been investigated. The temperature dependence of magnetic susceptibility, electrical resistivity, and specific heat show Kondo-lattice formation. Furthermore, a heavy Fermi-liquid state without magnetic ordering down to 2.0 K is found to evolve below about 6 K. The electronic specific heat coefficient γ is enhanced to values as large as to 550 mJ/mol ${\mathrm{K}}^2$. The magnetization measured up to 40 T at 1.6 K has a field dependence which is expected for a Kondo system when the total angular momentum is $J>\mathrm{}1.\mathrm{}$ All results are in good agreement with the extrapolation of the previous results of ${\mathrm{YbCu}}_{5-x}{\mathrm{Ag}}_x\hspace{0.5em}(0.125\mathrm{}<~x<~1.0)$ for $x\to 0$. The concentration dependence of characteristic temperatures of ${\mathrm{YbCu}}_{5-x}{\mathrm{Ag}}_x$ can be quantitatively explained by the chemical pressure effect within the compressible Kondo model for the full range of Ag concentration ( $0.0<~x<~1.0).$ The origins of Kondo-lattice formation in ${\mathrm{YbCu}}_4$Ag and the valence transition in ${\mathrm{YbCu}}_4$In are discussed.