Low temperature stability of 4O martensite in Ni49.1Mn38.9Sn12 metamagnetic Heusler alloy ribbons

•Transformation sequence in Ni49.1Mn38.9Sn12 ribbons is studied.•ferromagnetic L21 austenite phase transforms into 4O martensite at 242 K.•austenite persists to well below the TC of martensite.•4O martensite is stable to low temperature range.

The structural transformation sequence in Ni49.1Mn38.9Sn12 ribbons is studied using calorimetric, thermomagnetic, resistivity and in-situ XRD measurements. It is confirmed that the ferromagnetic L21 austenite phase transforms into 4O martensite at 242 K. The austenite phase persists in the sample to well below the TC of martensite. Upon further cooling the 4O martensite phase is stable down to the low temperature range, what is ascribed to its limited Ni/Mn and e/a ratios. On heating lattice constants assume lower values resulting from stress relief upon thermal cycling.