Crystal structure and thermodynamic properties of NdCu₄Au compound

We report the synthesis of the antiferromagnet cubic-type structure NdCu₄Au derived by substituting Au for Cu in the parent binary NdCu₅ compound. The room temperature X-ray diffraction analysis indicates a cubic MgCu₄Sn-type structure with space group F4¯3m (No. 216) for the NdCu₄Au compound. The thermodynamic properties of NdCu₄Au have been probed by magnetic susceptibility, χ(T), magnetization, M(_μ0H), and specific heat, C_p(T), measured down to 1.8 K. The low temperature χ(T) data shows probably an antiferromagnetic (AFM)-like anomaly associated with a Néel temperature T_N=3.9 K. In the paramagnetic region, χ(T) data follows the modified Curie-Weiss law with an effective magnetic moment _μeff=3.547(5)_μB and Weiss temperature _θp=-10.19(8)K. The value for μ_eff is close to the value of 3.62 μ_B expected for the Nd³⁺-ion. No evidence of metamagnetic transition was observed from the isothermal M(_μ0H) results. C_p(T) data confirm the AFM phase transition at T_N=3.5 K close to the value of 3.9 K observed in χ(T). The 4f-electron specific heat shows a Schottky-type anomaly around 20 K associated with crystalline-electric-field (CEF), with energy splitting Δ₁=62(5) K and Δ₂=109(9) K of the Nd³⁺ (J=9/2) multiplet, that are associated with the first and second excited state of Nd³⁺-ion. From the results of the 4f-electron magnetic entropy, it is speculated that the CEF ground state of Nd³⁺ (J=9/2) ions is the Γ₆ doublet for NdCu₄Au.