Conical incommensurate magnetic ordering in the transition metal-rich YCo12B6 ternary boride

The ternary boride YCo₁₂B₆ was investigated by means of ac susceptibility, magnetization, and neutron powder diffraction experiments over the temperature range 1.5 K – 300 K. The crystal structure was refined and the spin configuration determined. This intermetallic compound crystalizes in a rhombohedral $\left(\mathrm{R}\bar{3}\mathrm{m}\right)$$\left(\mathrm{R}\bar{3}\mathrm{m}\right)$ structure. In the ground state, its magnetic structure is characterized by a short incommensurate propagation vector k = (0, 0, $\pm$$\pm$0.0432), i.e., a long incommensurate period along the c-axis. Substantially different magnetic moments have been observed on the two crystallographically inequivalent Co sites (18 g and 18 h), a larger moment being refined on the Co-18h position. The Co spins arrange themselves into a conical magnetic structure with a tilt angle of about 57° with respect to the threefold symmetry axis c. Furthermore, a highly anisotropic lattice expansion is observed.