Magnetic properties of U2Co17−xSix single crystals

The homogeneity range of U2Co17−xSix system with the hexagonal Th2Ni17-type crystal structure extends from x = 1 to 3.4. The variation of the magnetic properties within the homogeneity range was studied on single crystals. All the compounds are ferromagnetic, Ms and TC decrease monotonously with increasing Si content. The strongly modified magnetic anisotropy of U2Co17−xSix, as compared to isostructural Lu2Co17−xSix with the non-magnetic Lu, points to a magnetic state of U up to x = 3.0. The U contribution to K1 decreases with increasing Si content and vanishes at x = 3.4 that can be treated as a transition from magnetic to non-magnetic state of U. Spin reorientation was observed with varying temperature in compounds with x ≤ 3 due to a competition of the U and Co sublattices anisotropies which occurs as two second-order phase transitions of the “plane–cone” and the “cone–axis” type.