Empirical mapping of Ni-Mn-Ga properties with composition and valence electron concentration

A range of Ni-Mn-Ga alloy compositions close to the stoichiometric Heusler composition, Ni2MnGa, has been reported to show field-induced strains of several percent. Such observations, and the magnitude of the strain observed, depend on the values of several critical material parameters, most importantly the martensitic transformation temperature (T-mart), Curie temperature (T-C), saturation magnetization (M-s), strength of the magnetocrystalline anisotropy, and the details of the martensite structure. Here, data collected from a variety of sources are plotted and their variations are fit with empirical formulas to afford a better overall picture of the behavior of this system. It is found that the martensitic transformation temperature is the parameter most sensitive to the composition; saturation magnetization appears to peak sharply at 7.5 valence electrons/atom, finally the composition field over which the saturation magnetization exceeds 60 emu/g, and 300 K <T-mart<T-C, has been explored only at the margins. (C) 2002 American Institute of Physics.