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

Abstract

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 Γ¹₂ 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 K_1(Tb) = (0.240,0.155,0.48) and K_1(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 μ_B.