Active material typically exhibit a twinned microstructure, in which a single crystal or grain is divided into different twin variants. Each of these variants has a different orientation of the unit cell, which separated by twin boundaries. When subjected to a mechanical stress or electric/magnetic field, one twin variant may expand at the cost of the other in a process named twinning .
Dynamic experiments that apply pulses of magnetic field are already well-established methods developed uniquely, and used successfully for measurements of twin boundary velocities and kinetic relations in FSMA NiMnGa at room temperature. In the framework of this research project, pulse magnetic field experiments were expanded to a range of temperatures, using a special non-conducting sample holder capable of heating/cooling the crystal inside the magnetic pulser. The range of temperatures that covered at this research is from up to the transformation temperature, which is about . Analysis of the experimental results leads to an identification of the relationship between motion of twin boundaries and temperature, and also the relationship between barriers/peierls energy and temperature. The kinetic behavior is similar in all tested temperature range i.e., a clear transition from slow to faster motion at a critical driving force. The value of the transition driving force (Peierls barrier) decreases as the temperature increase, but doesn`t go to zero at the transformation temperature. This observation is explained based on thermodynamic considerations. The obtained results have important implications on actuation, sensing, and energy harvesting applications that based on SMA.
