Crystal and Magnetic Structures of the Ternary HoNiSi and HoNiGe Compounds: An Example of Intermetallics Crystallizing with the ZrNiP Prototype.

We report two new rare-earth (R) ternary intermetallic compounds-HoNiT with T = Si and Ge-that correspond to the RNiT 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 ZrNiP-type structure with = 0.52; their stoichiometry, determined from both single-crystal and powder X-ray diffraction data, is centered on HoNiT 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, RNiT compounds also form for R = Y and Tb, representing the first examples of rare-earth-based compounds adopting the ZrNiP structural prototype. Bulk magnetization data reveal the main transitions of the ferrimagnetic or ferromagnetic type at = 38 K for HoNiSi and = 37 K for HoNiGe, which are followed by subsequent magnetic reordering at lower temperatures. Neutron diffraction shows complex magnetic structures below with both ferromagnetic and antiferromagnetic components and magnetic propagation vector κ = [0, 0, 0]. Below ≅ 24 K (22 K) for the silicide (germanide), an additional antiferromagnetic coupling following an incommensurate magnetic propagation vector κ = [κ, 0, 0] appears to coexist with the first magnetic structure.