Inverse magnetocaloric effect in Mn2NiGa and Mn1.75Ni1.25Ga magnetic shape memory alloys

Inverse magnetocaloric effect is demonstrated in Mn2NiGa and Mn1.75Ni1.25Ga magnetic shape memory alloys. The entropy change at the martensite transition is larger in Mn1.75Ni1.25Ga, and it increases linearly with magnetic field in both the specimens. Existence of inverse magnetocaloric effect is consistent with the observation that magnetization in the martensite phase is smaller than the austenite phase. Although the Mn content is smaller in Mn1.75Ni1.25Ga, from neutron diffraction, we show that the origin of inverse magnetocaloric effect is the antiferromagnetic interaction between the Mn atoms occupying inequivalent sites.