Magnetic structure determination of TbCo2Ni3using polarized and nonpolarized neutron powder diffraction

The structural (space group $P$6/mmtn) and magnetic parameters of TbCo${}_{2}$Ni${}_{3}$ are investigated using neutron powder diffraction and polarized neutron powder diffraction at several temperatures below the magnetic transition temperature. It is found that this compound orders ferrimagnetically at 315 K, with ferromagnetic Tb and Co/Ni sublattices. Below 100 K, the magnetic axis is perpendicular to the hexagonal axis. Above 100 K, the magnetic axis reorients slightly towards the hexagonal axis. The magnitudes and orientation of the ordered magnetic moments exhibit complex temperature dependences. The observed magnitude of the ordered Tb magnetic moment at $T$ $=$ 10 K, is found to be 8.1(2) ${\ensuremath{\mu}}_{B}$, smaller than the free Tb${}^{3+}$ ion. The significance of this property, and its relation to the mechanisms driving the magnetic order in the parent TbCo${}_{5}$ compound, are discussed.