Antiferromagnetism and mixed valency in the new Kondo lattice compound Ce3Rh4Sn7

Single crystals of a new ternary compound Ce3Rh4Sn7 were synthesized by flux method and its crystal structure and magnetic properties were studied by single crystal X–ray diffraction and magnetic susceptibility, specific heat and resistivity measurements. Ce3Rh4Sn7 crystallizes in a new monoclinic crystal structure, space group P21∕m (No. 11) with Z = 2 and lattice parameters a = 9.8708(5) Å, b = 4.5779(3) Å and c = 14.2381(7) Å, β = 109.535(5)∘, and V = 606.35(6) Å3. The structure exhibits three inequivalent Ce-sites. A striking structural motif is the tetragonal pyramid of Rh-ions surrounding the Ce2 yielding an extreme short Ce2–Rh1 spacing of d = 2.7486(10) Å. This strong hint to mixed valent cerium behavior is supported by the entropy analysis. We argue that the Ce2–ion is in a nonmagnetic Ce3+δ state while the other 2 Ce–sites are in a trivalent state. At low temperatures these latter become partially Kondo screened (TK ≈ 4 K) and order antiferromagnetic below TN = 2.31 K. The ordering is accompanied by a superzone gap-opening in direction of the magnetic propagation vector Q = (0, 0, l).