Giant inverse magnetocaloric effect near room temperature in Co substituted NiMnSb Heusler alloys

The effect of Co on the structural, magnetic and magnetocaloric effect (MCE) of Ni50-xCoxMn38Sb12 (x = 0, 2, 3, 4, 5) Heusler alloys was studied. Using x-ray diffraction, we show the evolution of the martensitic phase from the austenite phase. The martensitic transition temperature is found to decrease monotonically with Co concentration. Remarkable enhancement of MCE is observed near room temperature upon Co substitution. The maximum magnetic entropy change of 34 J kg-1 K-1 was achieved for x = 5 at 262 K in a field of 50 kOe and a value of 29 J kg-1 K-1 was found near room temperature. The significant increase in the magnetization with large magneto-structural coupling associated with the reverse martensitic transition is responsible for the giant MCE in these compounds.