Tuning sign and intensity of magnetocaloric effect by co doping NiMnGa alloys

We studied the composition dependence of the critical temperatures and of the magnetocaloric properties of Co doped NiMnGa alloys around the Mn-rich composition Ni50Mn30Ga20. By varying the Co and Mn content we have been able to tune the critical temperatures and to obtain a complete reverse martensitic transformation between paramagnetic martensite and ferromagnetic austenite. Unlike the Co-free alloys, high values of inverse magnetocaloric effect are associated to such a reverse transformation. The possibility to change the sign of the magnetocaloric effect by stoichiometric control of NiCoMnGa makes these materials interesting for magnetic refrigeration applications.