Structure and magnetic properties of Ni2(Mn,Co)Ga Heusler alloys rapidly solidified by melt-spinning

In this study microstructure and magnetic properties of cobalt substituted Ni2MnGa based ferromagnetic shape memory alloys (FMSA) are presented. Ni50Mn(25−x)CoxGa25 (x = 2, 5, 8, 11 at%) alloys were synthesized using the melt-spinning technique. Martensite, austenite and pre-martensitic tweed structures were found at room temperature for alloys containing 2, 5, 8 and 11% Co and melt-spun at two extreme wheels speeds viz., 20 m/s and 30 m/s. However, the alloy containing 5% Co melt-spun at a wheel speed of 20 m/s consists of 7 M or 14 layered Martensite phase. Magnetic properties such as saturation magnetization (Ms), martensitic transformation temperature (Tm) and Curie temperature (Tc) were measured and were found to be attractive for most of the melt-spun alloys containing higher “Co” concentrations. Upon annealing at 1273 K for 1 h, γ (gamma) phase was found to stabilize. The magnetic properties were found to correlate with the phase content of the Co substituted alloys.