Martensitic transformation and magnetic properties of Heusler alloy Ni–Fe–Ga ribbon

The martensitic transformation and magnetic properties of ferromagnetic shape memory alloy Ni50+ xFe25− xGa25 (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 L21 → B2 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 Ni2FeGa alloy that is a modulated martensite with small domain size. The influences of Fe substitution for Ni in Ni2FeGa on the saturation magnetization and exchange interaction are also discussed.  2004 Elsevier B.V. All rights reserved. PACS: 64.70.Kb; 75.50.Cc