Detailed discrimination of the order of magnetic transitions and magnetocaloric effect in pure and pseudobinary Co Laves phases

We present a study of the Banerjee criterion and its applicability to those cases in which the first- or second-order character of a magnetic phase transition is controversial. Detailed magnetization measurements on RCo2RCo2 (R=ErR=Er, Pr, Nd, and Dy) are analyzed in the framework of Landau theory and the Banerjee criterion. We show that, in general, a simple observation of the curvature of H/MH/M vs. M2M2 is not sufficient to determine the order of a magnetic transition. Our detailed analysis, together with a complementary calorimetric study, has also been applied to the pseudobinary solid solution ErxPr1−xCo2 (x=0.9x=0.9, 0.8, and 0.7), in order to check its validity in an unknown, non-trivial case. Magnetization measurements on ErxPr1−xCo2 compounds with x=0.6x=0.6 and 0.4 show that this analysis is restricted to single phase and unfrustrated magnets. We present also the magnetic entropy change at the transition of the studied RCo2RCo2 compounds obtained by applying the Maxwell relations.