Giant Magnetocaloric Effect in the Double-perovskite Gd2NiMnO6

We have synthesized single crystal of Gd$_{\mathrm{2}}$NiMnO$_{\mathrm{6}}$(GNMO) by the Bi-flux method and investigated magnetocaloric effect in them by magnetic measurements. Magnetic susceptibility of GNMO increases smoothly as temperature decrease and ferromagnetic order occurs below 135 K, and additional anomaly show at low temperature, indicative of the onset of Gd$^{\mathrm{3+}}$ spin arrangement. At the temperature, magnetic entropy change, -$\Delta $S$_{\mathrm{M}}$, with the field changes of 0-9 T, calculated from isothermal M(H) data using Maxwell relation, exhibits sharp peak. This peak is gigantic and cryogenic, these make GNMO promising cryogenic magnetic refrigerant materials.