Crystal and Magnetic Structures of the Ternary Ho(2)Ni(0.8)Si(1.2) and Ho(2)Ni(0.8)Ge(1.2) Compounds: An Example of Intermetallics Crystallizing with the Zr(2)Ni(1–x)P Prototype

[Image: see text] We report two new rare-earth (R) ternary intermetallic compounds—Ho(2)Ni(0.8)T(1.2) with T = Si and Ge—that correspond to the R(5)Ni(2)T(3) phase earlier reported to form in Dy–Ni–T and Ho–Ni–T ternary systems. The compounds crystallize in a filled version of the orthorhombic Zr(2)Ni(1–x)P-type structure with x = 0.52; their stoichiometry, determined from both single-crystal and powder X-ray diffraction data, is centered on Ho(2)Ni(0.8)T(1.2) with a narrow solid solubility range for the silicide, while the germanide appears to be a line phase. In addition to R = Dy and Ho, R(2)Ni(0.8)T(1.2) compounds also form for R = Y and Tb, representing the first examples of rare-earth-based compounds adopting the Zr(2)Ni(1–x)P structural prototype. Bulk magnetization data reveal the main transitions of the ferrimagnetic or ferromagnetic type at T(C) = 38 K for Ho(2)Ni(0.8)Si(1.2) and T(C) = 37 K for Ho(2)Ni(0.8)Ge(1.2), which are followed by subsequent magnetic reordering at lower temperatures. Neutron diffraction shows complex magnetic structures below T(C) with both ferromagnetic and antiferromagnetic components and magnetic propagation vector κ(1) = [0, 0, 0]. Below T(N) ≅ 24 K (22 K) for the silicide (germanide), an additional antiferromagnetic coupling following an incommensurate magnetic propagation vector κ(2) = [κ(x), 0, 0] appears to coexist with the first magnetic structure.