In a series of (Nd, Dy)Co2 and (Pr, Dy)Co2 compounds, the type of the magnetic phase transition
was studied by magnetization and electrical-resistivity measurements. In both systems, a cchange of type
was observed from second order (for NdCo2 and PrCo2) to first order (for compounds containing more than
about 20% Dy). The results are discussed in the Inoue-Shimizu model, generalized in such a way that the
presence of both light and heavy rare-earth atoms is taken into account. The volume dependence of the
parameter a3 (i.e. of the free-energy contribution a3M2
Co/4) is supposed to play a decisive role in the
determination of the order of the magnetic transition. ?? 1993.
