Successive phase transformation in ferromagnetic shape memory alloys Co37Ni34Al39 melt-spun ribbons

The martensitic transformation in Co$_{37}$Ni$_{34}$Al$_{29}$ ribbon is characterized in detail by means of in-situ thermostatic x-ray diffraction and magnetic measurements. The results show a structural transition from the body-centred cubic to martensite with a tetragonal structure during cooling. Comparison between the results of the diffraction intensity with the magnetic susceptibility measurements indicates that the martensitic transformation takes place in several different steps during cooling from 273 to 163~K. During heating from 313 to 873~K, the peak width becomes very wide and the intensity turns very low. The $\gamma$-phase (face-centred cubic structure) emerges and increases gradually with temperature increasing from 873 to 1073~K.