Discovery and Characterization of Antiferromagnetic UFe₅As₃

This work presents a study on a new uranium iron arsenide UFe₅As₃. By implementing Bi-flux synthesis, we were able to grow mm-sized single crystals of this compound, which show twinning. UFe₅As₃ is one of only two known uranium iron arsenides. It adopts a monoclinic, UCr₅P₃-type crystal structure (space group P2₁/m, Pearson symbol mP18, a = 7.050(2) Å, b = 3.8582(9) Å, c = 9.634(1) Å, β = 100.25(1)°). The magnetic susceptibility of UFe₅As₃ indicates it to be an antiferromagnet with T_N = 47 K and μ_eff = 4.94 μ_B per formula unit, signaling that both U and Fe are likely magnetic in this material. The material appears to be anisotropic, with a small (likely ferromagnetic) spin reorientation transition around T = 29 K. The Sommerfeld coefficient γ₀ = 135 mJ mol^-1 K^-2 suggests enhanced effective electron mass in UFe₅As₃, while electrical resistivity indicates metallic, Kondo-like behavior.