Magnetic behavior of uranium in strong ferromagnetic matrix of 3d-metals

Uranium does not form binary compounds with Fe and Co having the 2-17 stoichiometry, however, the hexagonal Th₂Ni₁₇-type crystal structure, which is characteristic for R₂T₁₇ with heavy rare-earth metals, can be stabilized by substitution of a small amount of third element, e.g. Si, for the T metal. In U₂(T,Si)₁₇ compounds, where a strong 5f-3d electron hybridization causing a delocalization of the 5f electrons is expected, the magnetic ordering of the U sublattice seems to be hardly possible. However, the single-crystal study of magnetic anisotropy U₂(T,Si)₁₇ compounds together with isostructural compounds of non-magnetic Lu gives arguments pointing to the magnetic contribution from the U sublattice. Results of magnetization studies of single crystals of U₂(Fe_1-xCo_x)_13.6Si_3.4 and U₂Co_17-xSi_x are discussed.