Exchange interaction in rare-earth compounds of the type RCo4B

The field dependence (up to 35 T) at 4.2 K of the magnetization of several compounds of the type _{R1−xYxCo4B (R = rareearth}) has been studied. The magnetic isotherms at 4.2 K are analysed with a mean-field model. The magnetic coupling constant J_RCo between the moments of the rare earth and cobalt in the Hamiltonian H = ∑_RCo2J_RCoS_R · S_co are shown to be more reliable than the coupling constants derived from a mean field analysis of the Curie temperatures for these compounds.