Implications of twinning kinetics on the frequency response in NiMnGa actuators

The explicit kinetic relation for twin wall motion in NiMnGa is used to correlate basic material properties to magneto-mechanical actuation rates in these crystals. In particular, we identify two parameters: the Peierls energy barrier and the twin wall mobility, which directly determine the dynamic response of NiMnGa actuators at frequencies above 10 Hz. Comparison between the kinetics of type I and type II twin walls reveals a correlation between the Peierls energy barrier and the commonly used twinning stress property. However, it is shown that twinning stress dictates twin wall dynamics only at very slow frequencies, typically below 1 Hz.