Magnetic Anisotropy of U₂(Fe_1-xCo_x)_13.6Si_3.4 (0≤x≤0.5)

Single crystals of the U₂(Fe_1-xCo_x)_13.6Si_3.4 (x=0, 0.1, 0.2, 0.3, 0.4, 0.5) solid solutions (hexagonal crystal structure of the Th₂Ni₁₇ type) were prepared for first time and their magnetization was measured at 4.2 K along the principal axes. The alloys exhibit a large basal-plane type magnetocrystalline anisotropy. Strong non-linearity of hard-direction magnetization curves and especially first-order magnetization process (FOMP) at low x values needs for description a large second anisotropy constant K₂ which cannot be provided by the Fe sublattice and is, therefore, a strong evidence for magnetic ordering of U sublattice. K₂ turns from negative to positive with increasing x at x = 0.2 which is reflected in disappearance of FOMP. The molecular spontaneous magnetic moments M_s decreases from 23 to 14 μ_B/f.u. whereas the Curie temperatures T_C increases from 530 K to 595 K with increasing x from 0 to 0.5.