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

Abstract Tb 0.75 Y 0.25 Co 3 B 2 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  μ B , unusually small relative to the free ion and parent compound (TbCo 3 B 2 ) values. These magnetic and crystal properties are discussed and compared with what was previously published for the parent compound.