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

Abstract

Magnetic measurements which have been performed on single crystals of the Gd${\mathrm{Co}}_2$, Ho${\mathrm{Ni}}_2$, and Ho${\mathrm{Co}}_2$ 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 have been determined from the magnetization variation in intense magnetic fields. The change of easy magnetization direction observed at 14 K on Ho${\mathrm{Co}}_2$ corresponds to a change, with temperature, of the level scheme of the ${}_{}{}^5{}_{}{}^{}J_8^{}{}_{}{}^{}$ ground-state multiplet. An entropy discontinuity is associated with this transition, leading to a specific-heat anomaly. For Ho${\mathrm{Co}}_2$, the values of the anisotropy constants at 0 K are $K_1=-{10}^7$ erg/${\mathrm{cm}}^3$ and $K_2={10}^9$ erg/${\mathrm{cm}}^3$. The interactions in Ho${\mathrm{Ni}}_2$ 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.