Microstructures and Magnetic Properties of Fe–Ga and Fe–Ga–V Ferromagnetic Shape Memory Alloys

The microstructures and magnetic properties of bulk Fe
₇₃
Ga
₂₇
and Fe
₇₃
Ga
₁₈
V
₉
(at.%) ferromagnetic shape memory (FSM) alloys were investigated by transmission electron microscopy (TEM), a magnetostrictive-meter setup, and a superconducting quantum interference device magnetometry. Results showed that in the Fe
₇₃
Ga
₂₇
FSM alloy solution treated (ST) at 1100°C for 4 h and quenched in ice brine, the antiphase boundary segments (APBs) of the D0
₃
domain were in the A2 (disordered) matrix and the Fe
₇₃
Ga
₂₇
FSM alloy had an optimal magnetostriction and a higher magnetostrictive susceptibility (Δλ
^s
_||
/ΔH). In Fe
₇₃
Ga
₂₇
FSM alloy ST, aged at 700°C for 24 h and furnace cooled (7 HTFC), D03 nanoclusters underwent phase transformation to an intermediate tetragonal phase (i.e., L1
₀
-like tetragonal martensite) via Bain distortion, and finally L12 (Fe3Ga) structures precipitated, as observed by TEM. The L1
₀
-like tetragonal martensite and L1
₂
phases in the aged Fe
₇₃
Ga
₂₇
FSM alloy drastically decreased the magnetostriction from positive to negative. However, by adding V into the Fe
₇₃
Ga
₂₇
alloy system to produce Fe
₇₃
Ga
₁₈
V
₉
FSM alloy ST and ageing at 7 HTFC, the phase transformation of D0
₃
to an intermediate tetragonal martensite phase and precipitation of L1
₂
structures were not found. The results indicate that the aged Fe
₇₃
Ga
₁₈
V
₉
FSM alloy maintained stable magnetostriction. However, the addition of V into the Fe
₇₃
Ga
₂₇
alloy system to produce Fe
₇₃
Ga
₁₈
V
₉
does not result in a higher saturation magnetization (Ms) or magnetocrystalline anisotropy energy constant (Ku) in the Fe
₇₃
Ga
₁₈
V
₉
FSM alloy.