10M martensite in Ni-Mn-Ga is an extraordinary system that exhibits a combination of twin mobility at very low driving forces (supermobility) and large magnetocrystalline anisotropy, which together allow the manipulation of the martensitic microstructure by an external magnetic field. The nature and origin of this phenomenon have not yet been fully elucidated, and the fundamental question remains unanswered – what mechanism distinguishes 10M modulated Ni-Mn-Ga martensite from other known martensites and what underpins these exceptional properties. In this contribution, we will present detailed experimental measurements of the elastic properties of 10M martensite (Fig. 1a) and their temperature evolution which can shed some light on the puzzle.

Experiments have shown that 10M martensite exhibits extreme elastic anisotropy with shear instability in the modulation-related directions, which clearly suggests the existence of a previously unknown relaxation mechanism. Through a detailed experimental study of the evolution of this shear instability with temperature, correlating these results with the evolution of the modulation vector obtained from structural measurements [2], and incorporating the recent understanding of the duality of wave modulation and nanotwinning in 10M martensite [3], this very unusual mechanism can be explained: it is based on shear deformation related to the propagation of the phase of the modulation (collective excitations known as phasons) within the 10M lattice (Fig. 1b). We will discuss the implications of this relaxation mechanism on the mobility of twin interfaces in 10M martensite and the potential for further experimental and theoretical study in Ni-Mn-Ga.

References

[1] K. Repček et al., Advanced Materials, 2024, 36 (39), art. no. 2406672.
[2] P. Veřtát et al., Journal of Physics Condensed Matter, 2021, 33 (26), art. no. 265404.
[3] P. Veřtát et al., https://arxiv.org/abs/2503.04379.

The authors acknowledge the support provided by the Ferroic Multifunctionalities project, supported by the Ministry of Education, Youth, and Sports of the Czech Republic. Project No. CZ.02.01.01/00/22_008/0004591, co-funded by the European Union.

Dr. Petr Sedlák