Magnetic properties of single crystals of GdCo2, HoNi2, and HoCo2

Magnetic measurements performed on single crystals of the GdCo2, HoNi2, and HoCo2 Laves phases lead to a quantitative analysis of the crystal-field effects on energy and magnetization anisotropies. The anisotropy due to cobalt is negligible. Crystal-field parameters were determined from the magnetization variation in intense magnetic fields. The change of easy magnetization direction observed at 140K on HoCo2 corresponds to a change, with temperature, of the level scheme of the 5J8 ground-state multiplet. An entropy discontinuity is associated with this transition, leading to a specific-heat anomaly. For HoCo2, the values of the anisotropy constants at 00K are K1 = -107 g/cm3 and K2 = 109 erg/cm3. Interactions in HoNi2 are weak compared to crystal-field effects; when a magnetic field is applied, the anisotropy increases so much that it is no longer possible to measure it