Magnetocaloric Effect of Ni56Mn18.8Ga24.5Gd0.7 Alloy

With the addition of Gd, the Ni56Mn18.8Ga24.5Gd0.7 alloy exhibits non-modulated martensite phase at room temperature. From the illustration of Gd microstructure, it can be found that Gd exists along the subgrain boundaries. Hence, the crystalline size decreases and the mechanical properties improve. Ac-susceptibility results show that Ni56Mn18.8Ga24.5Gd0.7 alloy still undergoes simultaneous structural and magnetic transitions and transforms from ferromagnetic martensitic phase to paramagnetic austenitic phase with increasing temperature. The maximum magnetic entropy change is 13.4 J · (kg·K)−1 under 1.9 T field at 338 K. The giant magnetocaloric effect found in Ni56Mn18.8Ga24.5Gd0.7 alloy is attributed to the concurrently occurring first-order structural- and magnetic-phase transitions.