Microstructures and magnetic properties of Fe-Ga and Fe-Ga-V ferromagnetic shape memory alloys

Summary form only given. The microstructures and magnetic properties of bulk Fe₇₃Ga₂₇ and Fe₇₃Ga₁₈V₉ (at.%) ferromagnetic shape memory alloys (FSMAs) were investigated by transmission electron microscopy (TEM), x-ray diffraction (XRD), a magnetostrictive-meter setup, and a superconducting quantum interference device (SQUID) magnetometer. Results showed that the Fe₇₃Ga₂₇ FSM alloy solution treated (ST) at 1100 for 4 h and quenched in ice brine, the antiphase boundary segments (APBs) of the D0₃ domain were in the A2 (disordered) matrix and the Fe₇₃Ga₂₇ FSM alloy had an optimal magnetostriction and a higher saturated magnetization (M_s). In Fe₇₃Ga₂₇ FSM alloy ST, aged at 700 for 24 h, and furnace cooled (7 HTFC), D0₃ nanoclusters underwent phase transformation to an intermediate tetragonal phase (i.e., L1₀-like tetragonal martensite) via Bain distortion, and finally L1₂ (Fe₃Ga) structures precipitated, as observed by TEM and XRD. The L1₀-like tetragonal martensite and L1₂ phases in the aged Fe₇₃Ga₂₇ FSM alloy drastically decreased the magnetostriction from positive to negative. However, adding V into the Fe₇₃Ga₂₇ alloy system to produce Fe₇₃Ga₁₈V₉ FSM alloy ST and aged at 7 HTFC, the phase transformation of D0₃ to an intermediate tetragonal martensite phase and precipitation of L1₂ structures were not found. The results indicate that the aged Fe₇₃Ga₁₈V₉ FSM alloy maintained stable magnetostriction. But, the V addition into the Fe₇₃Ga₂₇ alloy system to produce Fe₇₃Ga₁₈V₉, does not result in a higher saturation magnetization (M_s) or magnetocrystalline anisotropy energy co- stant (K_u) in the Fe₇₃Ga₁₈V₉ FSM alloy.