Martensitic transformation in ordering-treated Fe₇₄Ga₂₆ alloy

Peak magnetostriction of Fe_100-xGa_x with x around 27 has been attributed to shear modulus softening, analogues to the scenario for a martensitic transformation. Recently, stress-induced local six-layer modulated monoclinic (6 M) martensites have been investigated in Fe-Ga alloy. To identify the spontaneous martensitic transformation behavior, here we performed a comparative study of a Fe₇₄Ga₂₆ alloy with lower D0₃ ordering degree at the quenched state and with higher D0₃ ordering degree after subsequent long-term aging. In comparison with the quenched state that bears no martensites, the aged one undergoes spontaneous martensitic transformation upon cooling, and local 6 M martensites are observed after heating from liquid nitrogen temperature to room temperature. It is found that both the ordering degree and the structural stability of D0₃ phase are significantly improved after long-term aging, which makes the temperature-induced martensites visible. The present finding verifies that martensitic transformation is a universal phenomenon in the magnetostrictive Fe-Ga alloy.