Structure and Spin-Glass Magnetism of the Fe_1.5Ni_1.5Ga₄ Metallic Alloy

The Ga-rich region of the Fe-Ni-Ga ternary system was investigated, by exploring a line of compositions Fe_xNi_3-xGa₄, with 0.5 ≤ x ≤ 2.5. The single-phase cubic material was found only at the composition Fe_1.5Ni_1.5Ga₄ and its immediate vicinity, representing a new phase in the Fe-Ni-Ga diagram. The homogeneity range of this phase was estimated by additionally exploring a set of compositions Fe_xNi_yGa_z around the central composition Fe_1.5Ni_1.5Ga₄. The structural model was constructed based on the structure of the binary Ni₃Ga₄ parent phase, which crystallizes in the cubic Ia3̅d space group. We have considered that by substituting Fe for Ni, the Ia3̅d structure is preserved, with the Fe and Ni being statistically distributed at their 48g Wyckoff site. The possibility of a symmetry-reduced chiral structural model I4₁32 driven by chemical ordering of Fe and Ni cannot be entirely ruled out on the basis of the crystallographic study. The magnetic study of the Fe_1.5Ni_1.5Ga₄ phase has revealed that the material forms a spin glass phase below the spin freezing temperature T_f ≈ 9 K. Since the spin glass ordering of the Fe and Ni magnetic moments is compatible with their random distribution, the magnetic study supports the disordered cubic Ia3̅d model.