Antiferromagnetism and mixed valency in the new Kondo lattice compound CeRhSn

Opletal, P.  ; Duverger-Ndellec, E.*; Miliyanchuk, K.*; Malick, S.*; Hossain, Z.*; Custers, J.*

Single crystals of a new ternary compound CeRhSn 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. CeRhSn crystallizes in a new monoclinic crystal structure, space group 2m (No. 11) with Z = 2 and lattice parameters = 9.8708(5) , = 4.5779(3) ; and = 14.2381(7) , = 109.535(5), and V = 606.35(6) . 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 = 2.7486(10) . This strong hint to mixed valent cerium behavior is supported by the entropy analysis. We argue that the Ce2-ion is in a nonmagnetic Ce state while the other 2 Ce-sites are in a trivalent state. At low temperatures these latter become partially Kondo screened ( 4 K) and order antiferromagnetic below = 2.31 K. The ordering is accompanied by a superzone gap-opening in direction of the magnetic propagation vector Q = (0, 0, l).