Surface topography, microstructure and magnetic domains in Al for Sn substituted metamagnetic Ni–Mn–Sn Heusler alloy ribbons

• Ni–Mn–Sn ribbons show different surface anisotropies between top and bottom side.
• The easy magnetization axis of the ribbons lies in the rolling direction.
• 3Al sample has a characteristic microstructure typical for martensite phase.
• The martensitic plates are 70–100 nm in size.
• The ribbons show a magnetic multidomain structure.

Heusler alloy Ni48Mn39.5Sn12.5−xAlx (x = 0, 1, 2,3) ribbons were prepared by melt spinning. The cross section of ribbons reveals a typical heterogeneous microstructure consisting of small equi-axed and columnar grains. The top and bottom ribbons sides are homogenous in composition but they differ in terms of surface structure. The wheel ribbon side appears smoother and shows some degree of macroscopic organization. On the other hand the free ribbon surface regardless of composition shows a more complex morphology consisting of small equi-axed grains, larger grains forming clusters and conical sub crystal structures. A characteristic twinned plate like microstructure confirming the presence of an increased amount of martensite has been observed for the Ni48Mn39.5Sn9.5Al3 ribbon. The martensitic plates are 70–100 nm in size. The phase shift of 0.5° was detected, while scanning the latter ribbon sample in magnetic force microscope mode, indicating the existence of a magnetic multi-domain structure in this sample.