Magnetic and crystallographic study of Tb0.75Y0.25Co3B2

Tb0.75Y0.25Co3B2 was studied as a function of temperature by neutron powder diffraction, ac susceptibility and SQUID magnetization measurements. The solid solution, which is of hexagonal symmetry and is paramagnetic at 300 K, undergoes a magnetic Co-Co ordering transition at ∼150 K, and a second magnetic Tb-Tb ordering transition at ∼17 K. The latter induces a spin-reorientation transition, in which the magnetic axis rotates from the c-axis toward the basal plane. The component of the magnetic axis, which is perpendicular to c, leads to a crystal symmetry reduction from hexagonal to monoclinic. The observed magnitude of the magnetic moment of the Tb ion is 1.5 μB, unusually small relative to the free ion and parent compound (TbCo3B2) values. These magnetic and crystal properties are discussed and compared with what was previously published for the parent compound.