Atomic-size effect on the microstructural properties of Ni2FeGa

The microstructural properties of melt-spun ribbon of the ferromagnetic shape-memory Heusler alloy Ni2FeGa have been investigated by transmission electron microscopy. Two kinds of micromodulated structures, Fe-rich and Ga-rich, have been established. The Fe-rich micromodulated structure is formed by Fe atoms partially replacing Ga atoms on {3 5 0} planes in the L21 structure. The Ga-rich micromodulated structure concerns Ga atoms partially replacing Fe atoms on {3 + n, 5 + n, 0}(n ⩾ 0) planes. The Fe-rich and Ga-rich micromodulated structures originate from spinodal decomposition of the Fe and Ga compositions, which is closely related to the difference of atomic sizes of Ni, Fe and Ga.