Martensitic transformation and magneto-strain in melt spun NiMnGaAl Ferromagnetic Shape Memory Alloys

Ni55Mn22Ga23−xAlx (0 ≤ x ≤ 5) melt spun ribbons homogenized at 1073 K for 30 h exhibited an elevation in martensitic transformation onsets and a reduction in Curie temperature with increase in Al content. The phenomenon has been attributed to different site occupancy by Al, exchange coupling and paramagnetic martensite during thermal and magnetic transitions. Transmission Electron microscopy revealed systematic patterns of dislocations in alloy with x = 1, which become denser at high Al content. X = 1 alloy revealed high magnetic field induced strain (MFIS) value it is attributed to a critical combination of austenite and martensite phase.