Magnetic coupling in CaCu5-type rare-earth cobalt compounds

The composition of rare-earth cobalt compounds of the hexagonal CaCu5-structure type varies from RCo5 to approximately RCo6 when passing through the lanthanide series. We have studied the field dependence (up to 35 T) at 4.2 K of the magnetization of several compounds of this series, including various pseudobinary compounds of the type R1-xYxCo5+δ and GdCo5-rNir. The magnetic isotherms at 4.2 K were analyzed with a mean-field model. The magnetic coupling constant JRT between the moments of the rare-earth (R) and 3d (T) element in the Hamiltonian H = -Σ2JRTSR·ST derived from these measurements was found to have a tendency to decrease with increasing atomic number of the lanthanide involved