From Tb 3 Ni 2 to Tb 3 CoNi: The interplay between chemistry, structure, and magnetism

Formation, crystal structure, and macroscopic and microscopic magnetism of the binary Tb 3 Ni 2 and derivative pseudobinary Tb 3 CoxNi 2-x phases have been investigated using an array of experimental methods. While Tb 3 Ni 2 crystallizes in the monoclinic Dy 3 Ni 2 structure type (mS20, C2/m), the substitution of Co for Ni results in a structural transition into the rhombohedral Er 3 Ni 2 type (hR45, R3?h) at x(Co)?0.34 and beyond in the Tb 3 CoxNi 2-x system. In both the monoclinic and rhombohedral phases, the addition of Co leads to an anisotropic change of lattice parameters and unexpected reduction of the cell volume. Measurements of bulk properties reveal that these compounds order ferrimagnetically or ferromagnetically at about 100 K. Complex noncollinear ferromagnetic ordering in the Tb sublattices is weakly dependent on composition. For x > 0.34 the long-range magnetic ordering leads to a strong anisotropic magnetostriction accompanied by a symmetry reduction from rhombohedral to triclinic. © 2019 American Physical Society.