The effect of non-magnetic dilution of the Tb sublattice in TbCo3B2

Solid solutions of Tb1-xYxCo3B2 (x = 0.05, 0.1, 0.25, 0.4 and 0.5) were studied by neutron powder diffraction, x-ray diffraction, AC susceptibility and SQUID magnetization measurements. Their magnetic and crystallographic properties were deduced and examined together with those previously published for the end compounds (x = 0, 1). These solid solutions have hexagonal symmetry and are paramagnetic at RT, and undergo a magnetic ordering transition of the Co sublattice, with the magnetic moments along the hexagonal axis, at T-Co similar to 150(15) K, independent of Y concentration. A second magnetic ordering transition of the Tb sublattice T-Tb <= 30 K accompanied by the rotation of the magnetic moments towards the basal plane, was observed for solid solutions with Y concentration x <= 0.25. This transition was also found to be accompanied by a crystallographic symmetry decrease. Unexpectedly, neutron powder diffraction showed that the magnitude of the ordered magnetic moment of the Tb ion decreases with Tb concentration.