Hysteretic structural changes within five-layered modulated 10M martensite of Ni–Mn–Ga(–Fe)

• Published in: Journal of physics. Condensed matter Vol. 33; no. 26; pp. 265404 - 265414
• Main Authors: Veřtát, P, Seiner, H, Straka, L, Klicpera, M, Sozinov, A, Fabelo, O, Heczko, O
• Format: Journal Article
• Language: English
• Published: England IOP Publishing 28.05.2021
• Subjects: ferromagnetic shape memory; microstructure; phase transformations; structural modulation; twinning; twinning; ferromagnetic shape memory; phase transformations; microstructure; structural modulation
• ISSN: 0953-8984; 1361-648X
• DOI: 10.1088/1361-648X/abfb8f

Modulated structure of Ni-Mn-Ga-based alloys is decisive in their magnetic shape memory functionality. However, the precise nature of their five-layered modulated 10M martensite is still an open question. We used X-ray and neutron diffraction experiments on single crystals to investigate structural changes within 10M-modulated martensite of the Ni Mn Ga Fe magnetic shape memory alloy. The modulation vector gradually increases upon cooling from commensurate = (2/5) , where is the reciprocal lattice vector, to incommensurate with up to pseudo-commensurate = (3/7) . Upon heating, reverse changes are observed with a thermal hysteresis of ≈ 60 K. The same hysteretic behaviour was detected in the electrical resistivity and the effective elastic modulus. Scanning electron microscopy showed that the changes are accompanied by the refinement of the / laminate. These observations indicate that the commensurate state is a metastable form of 10M martensite. Upon cooling, this phase evolves through nanotwinning into a more irregular and more stable incommensurate structure.