Techniques to characterize ternary and quaternary ferromagnetic shape memory alloys

Abstract

Ni-Mn-X (X = group IIIA-VA elements) Heusler alloys have been seen to exhibit multiferroic effects such as magnetic/metamagnetic shape memory (MSM/MMSM), magnetocaloric (MC), direct energy conversion etc. and have a large potential for diverse applications in actuation, magnetic refrigeration and conversion of low grade waste heat into electricity. Beneath the multifunctional potential of these alloys is a magnetostructural coupling encompassing structural and magnetic transformations, which in turn depends on alloy compositions. As compositions are varied different crystal structures are evolved and it becomes essential that the structures are accurately characterized for their microstructures. This paper provides a short review of characterization techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) with examples from our work as well as literature. Emphasis is laid on XRD, TEM and DSC, which are very important for microstructural characterization.

Keywords:

• Heusler alloys
• martensitic transformation
• austenite
• modulated martensite and microstructural characterization

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Notes

1 Intermartensitic transformations happen when the martensitic phase transforms to other modulated phases at lower temperatures. These are important because reversal back to the original martensitic phase may be difficult and may lead to loss of magnetic shape memory effect.