Abstract
The martensitic transformation and magnetic properties of ferromagnetic shape memory alloy Ni 50+ x Fe 25− x Ga 25 ( x = − 1 , 0, 1, 2, 3, 4) ribbons have been systematically studied. It has been found that with the increase of Ni concentration, the martensitic transformation temperature increases, but the Curie temperature decreases. Both the two-step thermally induced structural transformation and the one-step transition have been observed in NiFeGa alloys with different compositions. It is found that the two-step transition became the one-step transition after the ribbon being heat treated at 873 K or higher. X-ray diffraction patterns show that only L 2 1 → B 2 transition occurs in the samples treated at 873 K, while the γ phase will form in the samples treated at higher temperature. Transmission electron microscopy (TEM) studies show that the alloys with martensitic transformation temperature above the room temperature are non-modulated martensite with the large domain size, being different from the stoichiometric Ni 2FeGa alloy that is a modulated martensite with small domain size. The influences of Fe substitution for Ni in Ni 2FeGa on the saturation magnetization and exchange interaction are also discussed.
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