Magnetic structures of rare earth intermetallic compounds RCuAs2 (RÂ =Â Pr, Nd, Tb, Dy, Ho, and Yb)

Neutron scattering studies have been carried out on polycrystalline samples of a series of rare earth intermetallic compounds RCuAs2 (R = Pr, Nd, Dy, Tb, Ho and Yb) as a function of temperature to determine the magnetic structures and the order parameters. These compounds crystallize in the ZrCuSi2 type structure, which is similar to that of the RFeAsO (space group P4/nmm) class of iron-based superconductors. PrCuAs2 develops commensurate magnetic order with K = (0, 0, 0.5) below TN = 6.4(2) K, with the ordered moments pointing along the c-axis. The irreducible representation analysis shows either a Γ12 or Γ13 representation. NdCuAs2 and DyCuAs2 order below TN = 3.54(5) K and TN = 10.1(2) K, respectively, with the same ordering wave vector but the moments lying in the a-b plane (with a Γ29 or Γ210 representation). TbCuAs2 and HoCuAs2 exhibit incommensurate magnetic structures below TN = 9.44(7) and 4.41(2) K, respectively. For TbCuAs2, two separate magnetic ordering wave vectors are established as K1(Tb) = (0.240,0.155,0.48) and K2(Tb) = (0.205, 0.115, 0.28), whereas HoCuAs2 forms a single K(Ho) = (0.121, 0.041, 0.376) magnetic structure with 3rd order harmonic magnetic peaks. YbCuAs2 does not exhibit any magnetic Bragg peaks at 1.5 K, while susceptibility measurements indicate an antiferromagnetic-like transition at 4 K, suggesting that either the ordering is not long range in nature or the ordered moment is below the sensitivity limit of ≈0.2 μB.