Antiferromagnetic order and crystalline electric field in noncentrosymmetric hexagonal R E Ru 6 As 4 ( R E = Sm and Yb )

We investigated the electronic properties of RERu₆As₄(RE=La, Ce, Sm, and Yb) using single-crystalline samples grown by the Bi-flux method. These compounds crystallize in the noncentrosymmetric hexagonal LiCo₆P₄-type structure, featuring chain-like and triangular arrangements of magnetic $RE$ ions. From the electrical resistivity, magnetic susceptibility, and specific heat measurements, we have found that SmRu₆As₄ and YbRu₆As₄ order antiferromagnetically below the N\'eel temperature of 1.5 and 9.5 K, respectively. Despite the relatively high transition temperature of YbRu₆As₄, its magnetic field-temperature phase diagram reveals that the antiferromagnetic state collapses at a low field of μ₀Hc=1.70.28em0exT, accompanied by an unusual nonlinear magnetization. The small critical field and characteristic magnetization curve in YbRu₆As₄ suggest an important role of competing interactions associated with magnetic frustration.