R[formula omitted] ([formula omitted] Ce, Yb): New intermetallic compounds in the [formula omitted] stoichiometry series

Abstract

The orthorhombic, space group CmcmYbFe2Al10 structure type series of compounds are known to form with practically the entire series of rare-earth elements R, but only with the three d− electron elements Fe, Ru, and Os. The Ce-derivatives in particular have been of much interest since the first reports of their highly unusual physical properties. Classified as Kondo insulators, CeRu2Al10 and CeOs2Al10 controversially order magnetically and with uncharacteristically high Néel temperatures of ≃28 K. CeFe2Al10 on the other hand shows pronounced semiconducting and Kondo features but remains paramagnetic. As part of our ongoing studies into the rich physics of this class of materials we have succeeded in synthesizing new members of the 1:2:10 stoichiometry involving the chemical element Rh for the first time. CeRh2Al10 is found to crystallize in the tetragonal system with space group I41/amd. Yb Rh2Al10 on the other hand forms in the serial Cmcm orthorhombic structure type. We discuss important similarities between the two types. At 5.310Å the shortest Ce–Ce distance is, likewise to the situation in CeRu2Al10 and CeOs2Al10, also well above the Hill limit of 3.40Å. Despite the cage-like structure and large rare-earth separation distances, this study reveals the onset of long-range magnetic ordering in CeRh2Al10 at 3.9 K. The magnetic ordering develops out of an incoherent Kondo state that dominates the electrical resistivity below about 40 K.