Evidence for magnetic state of uranium in U2(Fe1−xCox)13.6Si3.4

Single crystals of solid solutions U2(Fe1−xCox)13.6Si3.4 (0 ≤ x ≤ 1) having the hexagonal Th2Ni17 crystal structure were grown by a Czochralski method. Magnetization measurements along the principal axes reveal the easy-plane magnetic anisotropy in compounds with x up to 0.95, whereas terminal compound U2Co13.6Si3.4 has the uniaxial anisotropy. Magnitudes of the anisotropy constants K1 and K2 for x up to ∼0.8 are high enough to suggest a U contribution to the anisotropy, i.e., a magnetic state of U. The observed rapid weakening of the anisotropy and the change of its type at highest Co content are attributed to the 3d-metal sublattice, namely to the considerable change of c/a ratio at the FeCo substitution in the “dumbbells”.