Magnetothermal properties of Gd$_{1-x}$Y$_x$Ni$_2$ compounds

The heat capacity of pseudobinary intermetallic compounds Gd$_{1-x}$Y$_x$Ni$_2$ (0 $\le x\le$ 1) has been studied. The magnetic contribution to the total heat capacity is isolated with the use of the data obtained for the paramagnetic analogs Lu$_{1-y}$Y$_y$Ni$_2$ possessing the same molar masses as the gadolinium compounds. It has been found that the difference between the entropies of the Gd$_{1-x}$Y$_x$Ni$_2$ ($x<$ 0.8) compounds and the corresponding paramagnetic Lu$_{1-y}$Y$_y$Ni$_2$ analogs reaches larger values than those expected from the calculations performed under the assumption that only Gd ions contribute to the magnetic part of the total entropy. The existence of an additional contribution of magnetic nature to the entropy of the Gd$_{1-x}$Y$_x$Ni$_2$ compounds, as well as the large values of the $\gamma$ coefficient in the linear-in-temperature term of the heat capacity, is assigned to the spin fluctuations induced by the $f$–$d$ exchange in the subsystem of Ni 3$d$ electrons.