Structure and Spin-Glass Magnetism of the Fe 1.5 Ni 1.5 Ga ₄ Metallic Alloy

The Ga-rich region of the Fe-Ni-Ga ternary system was investigated, by exploring a line of compositions FexNi3-xGa₄, with 0.5 ≤ x ≤ 2.5. The single-phase cubic material was found only at the composition Fe1.5Ni1.5Ga₄ 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 FexNiyGaz around the central composition Fe1.5Ni1.5Ga₄. The structural model was constructed based on the structure of the binary Ni₃Ga₄ parent phase, which crystallizes in the cubic Ia 3̅ d space group. We have considered that by substituting Fe for Ni, the Ia 3̅ d 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 Fe1.5Ni1.5Ga₄ phase has revealed that the material forms a spin glass phase below the spin freezing temperature Tf ≈ 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 Ia 3̅ d model.