High temperature atomic rearrangements in melt-spun Ni–Mn–Ga ribbons

The characteristic martensitic transformation (MT) temperatures and the Curie point of two melt-spun Ni52.5Mn24.5Ga23 (at.%) and Ni49.5Mn30.5Ga20 ribbons (10 mm wide, 50 μm thick) were analyzed by differential scanning calorimetry, susceptibility and thermogravimetric analysis (TGA). The temperature dependence of the TGA magnetic signal reflects the parallel changes in the magnetic susceptibility (i.e. an increase associated with the martensite to austenite transformation and a sharp decrease around the Curie point during the heating process). High temperature anneals performed on the as-cast melt-spun ribbons promotes an increase in the MT and Curie transition temperatures and in the enthalpy associated with the MT. This shift towards higher values is interpreted as a consequence of the atomic rearrangements (ordering process) that take place in the as-cast ribbons under the performed thermal treatment.