Composition dependence of magnetic and magnetothermal properties of Ni-Mn-Ga magnetic shape memory alloys

A simultaneous magnetic and structural transition is found for Ni2+xMn1xGa at 0.18x0.2. The existence of a composition range for observing the co-occurrent transition and the composition dependence of the critical temperatures are discussed in the light of the expected difference between the Curie temperatures of the austenitic and martensitic phases. A giant magnetic entropy change is deduced for the three samples, with a maximum value of the order of |Sm|= 15 J/kg K for a field span of 1.8 T.