Antiferromagnetic rare earth coupling in Pr_1-xTb_xNi and Nd_1-xTb_xNi single crystals

Magnetization and specific heat measurements were carried out on pseudo-binary Pr_1-xTb_xNi (x = 0.0, 0.1) and Nd_1-xTb_xNi (x = 0.0, 0.05, 0.1, 0.15) single crystals. The magnetic transition temperatures for Pr_1-xTb_xNi increased with x, whereas those for Nd_1-xTb_xNi decreased slightly as x increased. The effective magnetic moments, deduced from the temperature dependence of susceptibility, increased with x for both systems. The saturation magnetizations observed at the magnetically easy directions for all samples suggest that the magnetic coupling between the Pr (or Nd) and Tb moments is antiferromagnetic. A noticeable increase in magnetization in higher external field, onset at 5 T, is observed for Pr_0.9Tb_0.1Ni and indicates that there is a rearrangement of the magnetic moments. Calculations of the crystal electric field effect of Pr and Tb in Pr_1-xTb_xNi were carried out using a simple point-charge model.