Magnetic and thermodynamic properties of GdCu₄Au

The results of magnetic susceptibility, χ(T), magnetization, σ(μ₀H), and specific heat, C_P (T), for GdCu₄Au are presented. The room temperature powder X-ray diffraction studies indicate a cubic MgCu₄Sn-type crystal structure with space group F3m (No.216). The low field dc χ(T) data shows an antiferromagnetic-like (AFM) anomaly associated with a Néel temperature T_N =10.8 K for GdCu₄Au. In the paramagnetic region above T_N, χ(T) data follows the Curies-Weiss law with an effective magnetic moment μ_eff =7.444(1) μ_B and paramagnetic Weiss temperature θ_P =-15.01(2) K. The experimental value of is close to the calculated value of 7.94 μ_B expected for the free Gd³⁺-ion. The field-cooled (FC) and zero-field-cooled (ZFC) χ(T) data provide evidence for the formation of spin-glass state with a freezing temperature T_f =15 K. σ(μ₀H) measured in the ordering region (below TN) shows that GdCu₄Au undergoes metamagnetic transition above 0.7 T, characterized by a slight upward curvature above this field. Measurement of σ(μ₀H) in the paramagnetic regions show a linear behaviour up to 0.7 T and a downward curvature at high fields. C_P (T) data shows an AFM-like phase transition at T_N =10.4 K close to the phase transition observed in χ(T) results. The 4f-electron entropy reaches the value of Rln2 close to T_N at 9.02 K and reaches the value of Rln(2J + 1) at T =180 K.