Phase Transitions and Magnetocaloric Effects in GdNi$_{2}$Mn$_{X}$*

The structural and magnetic properties of the GdNi$_{2}$Mn$_{x}$ system (for x $=$ 0.5, 0.6, 0.8, 1.0, 1.2, 1.4, 1.5) have been studied by x-ray diffraction and magnetization measurements. A rhombohedral PuNi$_{3}$-type structure was observed in the XRD data. A second order magnetic phase transition from ferromagnetic (FM) to paramagnetic (PM) was found, characterized by a long-range exchange interaction as predicted by mean field theory. A magnetic entropy change of $| \Delta $S$_{M}| = $ 3.1 J/kg K and 2.9 J/kg K for $\Delta $H $=$ 5 T was observed in the vicinity of the Curie temperature (T$_{C})$ for GdNi$_{2}$Mn$_{0.8}$ and GdNi$_{2}$Mn$_{1.4}$ respectively. In spite of the low values of $\Delta $S$_{M}$, the relative cooling power (RCP) was found to be 176 J/Kg for the GdNi$_{2}$Mn$_{0.8}$ compound. .