Application of a bi-stable chain model for the analysis of jerky twin boundary motion in NiMnGa

The "jerky" motion of a twin boundary in the ferromagnetic shape memory alloy NiMnGa is studied experimentally and theoretically. We employ a bi-stable chain model in order to interpret macroscopic stress-strain experiments and extract important micro-level properties. The analysis reveals the existence of a periodic barrier for type I twin boundary motion with an average distance of 19 mu m and amplitude of 0.16 J/m(2). Further, we show that the macroscopic mechanical response depends on the length of the crystal and predict a significant decrease of the hysteresis in sub-mm length specimens. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4773995]