Martensitic transformation behavior under magnetic field in Co-Ni-Al ferromagnetic shape memory alloys

Effect of the magnetic field on the martensitic transformation of Co-Ni-Al single-crystal was investigated by differential thermal analysis (DTA) and the in-situ microstructure observation under magnetic field. The martensitic transformation temperatures Ms and Mf of the Co34.5Ni35.5Al30 single-crystal specimen showing the martensitic transformation from the paramagnetic austenite (B2) to the ferromagnetic martensite slightly increased under the magnetic field and those temperature shifts were about 1.3°C at 1.0T. It was also observed in the Co34.5Ni35.5Al30 single-crystal specimen that the phase boundaries between the austenite and the martensite slightly move by applying the magnetic field of 1.0T. These results are discussed on the basis of a thermodynamic stabilty of the martensite phase under the magnetic field. The martensitic and the magnetic transformation behaviors of the Ni-Al-Co alloys are also reviewed.