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.