Discovery and Characterization of Antiferromagnetic UFe 5 As 3 .

This work presents a study on a new uranium iron arsenide UFe ₅ As ₃ . By implementing Bi-flux synthesis, we were able to grow mm-sized single crystals of this compound, which show twinning. UFe ₅ As ₃ is one of only two known uranium iron arsenides. It adopts a monoclinic, UCr ₅ P ₃ -type crystal structure (space group P 2 ₁ / m , Pearson symbol mP 18, a = 7.050(2) Å, b = 3.8582(9) Å, c = 9.634(1) Å, β = 100.25(1)°). The magnetic susceptibility of UFe ₅ As ₃ 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 γ ₀ = 135 mJ mol ^-1 K ^-2 suggests enhanced effective electron mass in UFe ₅ As ₃ , while electrical resistivity indicates metallic, Kondo-like behavior.