FERROMAGNETISM IN TbF 3

Magnetization measurements are reported on crystals of orthorhombic TbF3. Evidence of ferromagnetism is found at T < Tc = (3.95 ± 0.05) °K, with a saturation moment along a of 8 µB/Tb3+. A field-induced magnetic transitions is observed for H || c. The data are interpreted with a two-sublattice model in which magnetic moments of 9 µB/Tb3+ are fixed by the crystal field at angles ± (27 ± 2)° from the a axis in the c-a plane.