Effect of strong static magnetic field on the microstructure and transformation temperature of Co–Ni–Al ferromagnetic shape memory alloy

The effect of strong static magnetic field (SSMF) on the microstructure and phase transformation temperature of Co38Ni33Al29 ferromagnetic shape memory alloy during heat treatment has been studied. Results indicate that the microstructure and phase transformation temperature are significantly affected by the external SSMF. With the increasing magnetic field intensity, the volume fraction of γ phase decreased from 13.2 to 5.1%, the morphologies of γ phase evolved from rods to discrete stripes, and a clear alignment of γ phase was observed. In addition, the transformation temperatures are also elevated as the magnetic field intensity increases. The martensitic transformation temperature (MS) and the Curie point (TC) rose by 13 K and 10 K respectively when 4 T SSMF was applied. Moreover, the coercivity (HC) dramatically reduced to 11.7 Oe at 4 T magnetic field. Magnetic domains formed in β phase and they became ordered with the enhancing intensities of magnetic field.