Magnetic Properties of a TmCo 2 Single Crystal

The magnetization of a spherical single crystal of the ferrimagnetic TmCo 2 compound has been studied in fields up to 140 kOe. Below the ordering temperature (4 K ≦ T c ≦ 7 K depending on the melting method) the easy magnetization axis is [111]. Using the fact that the difference in the anisotropy energy between the [111] and [110] axis is very small, the relative importance of fourth and sixth order terms of the crystalline potential has been estimated. The existence of a singlet ground state explains the low spontaneous magnetization observed at 1.5 K.