Large anisotropy in Dy0.73Tb0.27Fe1.5Co0.5H 0.5 when compared with Dy0.73Tb0.27Fe1.5Co0.5 has been attributed to the orientational ordering of hydrogen atoms in the lattice. Pinning effects and discontinuous jumps in magnetization have been observed at 4.2 K, up to a magnetic field of 2 kOe. The former is due to domain wall pinning and the latter is due to spin-flip metamagnetism in a field-induced transition from a modulated phase to an equal-moment phase at low temperatures. © 1997 Elsevier Science S.A.