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

Abstract

The microstructures and magnetic properties of bulk Fe73Ga27 and Fe73Ga18V9 (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 Fe73Ga27 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 A 2 (disordered) matrix and the Fe73Ga27 FSM alloy had an optimal magnetostriction and a higher magnetostrictive susceptibility ( $\Delta \lambda^{s}_{\|} \Delta {H}$ ). In Fe73Ga27 FSM alloy ST, aged at 700 °C for 24 h and furnace cooled (7 HTFC), $D0_{3}$ nanoclusters underwent phase transformation to an intermediate tetragonal phase (i.e., $L1_{0}$ -like tetragonal martensite) via Bain distortion, and finally $L1_{2}$ (Fe3Ga) structures precipitated, as observed by TEM. The $L1_{0}$ -like tetragonal martensite and $L1_{2}$ phases in the aged Fe73Ga27 FSM alloy drastically decreased the magnetostriction from positive to negative. However, by adding V into the Fe73Ga27 alloy system to produce Fe73Ga18V9 FSM alloy ST and ageing at 7 HTFC, the phase transformation of $D0_{3}$ to an intermediate tetragonal martensite phase and precipitation of L 12 structures were not found. The results indicate that the aged Fe73Ga18V9 FSM alloy maintained stable magnetostriction. However, the addition of V into the Fe73Ga27 alloy system to produce Fe73Ga18V9 does not result in a higher saturation magnetization ( $M_{s}$ ) or magnetocrystalline anisotropy energy constant ( $K_{u}$ ) in the Fe73Ga18V9 FSM alloy.