A ternary intermetallic compound, U${}_3$Ru${}_4$Al${}_{12}$ in a single-crystal form, was studied by measurement of susceptibility, magnetization, electrical resistivity, magnetoresistivity, thermopower, and heat capacity, as well as neutron diffraction, revealing that this aluminide is an antiferromagnetically ordered ($T_{\mathrm{N}}$ $=$ 9.5 K) dense Kondo system ($T_{\mathrm{K}}$ ≈ 30 K) with a considerable enhancement of the Sommerfeld coefficient $\gamma$(0) of about $200{\mathrm{mJ}\mathrm{mol}}_{\mathrm{U}}^{-1}{\mathrm{K}}^{-2}$. The electrical resistivity and thermopower of U${}_3$Ru${}_4$Al${}_{12}$ show characteristic features of the interplay between anisotropic magnetic exchange, Kondo, and crystal field effects. A pronounced in-plane anisotropy and a unique noncollinear antiferromagnetic structure in the (a,b) hexagonal plane, found by neutron diffraction, are discussed in view of the effect of geometrical frustration caused by the distorted kagome lattice of a Gd${}_3$Ru${}_4$Al${}_{12}$-type crystal structure. Thus, the overall behavior of U${}_3$Ru${}_4$Al${}_{12}$ resembles that observed for the orthorhombic compound UCu${}_5$In, reported earlier as a spin density wave material.

• Received 25 July 2011

DOI:https://doi.org/10.1103/PhysRevB.85.064412