Magnetic properties and structural phase transformations of NiMnGa alloys

The magnetic properties and structural phase transformations of Heusler all oys M2+xMn1-xGa and Ni2-xMn1+x/2Ga1+x/2 were investigated. It was found tha t the martensitic transformation temperature increases and the Curie temper ature decreases with decreasing Mn concentration in the Ni2+xMn1-xGa system , but the magnetic properties decrease faster than those do in the Ni2-xMn1 +x/2Ga1+x/2 system. It suggests that the influence of the conduction electr on concentration and the distance between Mn atoms on the Curie temperature is stronger than the magnetic dilution effect. The martensitic transformat ion temperature shows a peak value at x = 0.06 in the Ni2-xMn1+x/2Ga1+x/2 s ystem. A large stress-free magnetic-field-induced strain (MFIS) of 1.8% has been obtained at room temperature in a single crystal sample with the comp osition in the first system.