W3CoB3-type {Y, Gd - Ho}3Co4−xAlx (x=0.5−1) rare earth compounds: Specific features of crystal structure and magnetic ordering

Neutron diffraction study in zero applied field shows mixed ferro-antiferromagnetic ordering of Tb3Co3.25Al0.75 with a wave vector K0=[0, 0, 0]. Below ~ 137 K Tb3Co3.25Al0.75 exhibits non-collinear ferrimagnetic ordering of terbium and cobalt sublattices with resulting of b-axis ferromagnetic and c-axis antiferromagnetic components of Cmc′m={1, mx}×{1, mz/[0, 0, 1/2]}×{1, i′} ×{1, 1/[1/2, 1/2, 0]} magnetic space group. The spin-reorientation transition in Tb3Co3.25Al0.75 below ~38 K corresponds to appearance of additional a-axis ferromagnetic component and decreasing of symmetry of magnetic ordering down to C2′/c={1, mz/[0, 0, 1/2]}×{1, i′}×{1, 1/[1/2, 1/2, 0]} magnetic space group.242