Kinetics of twin boundary motion in ferromagnetic shape memory alloys

In-situ neutron and synchrotron studies have played an important role in elucidating microscopic insights of deformation behaviors at multi length scales. We have recently applied the techniques to study ferromagnetic shape memory alloys (FSMAs), which have shown tremendous potential for applications of next-generation smart devices due to their exceptionally large magnetic-field-induced strains. Unlike in conventional shape memory alloys, in which a martensitic phase transformation occurs, in FSMA the shape memory effect is driven by twin boundary motion of the martensitic phase, leading to reorientation of the crystallographic twin variants. Using time-resolved neutron and synchrotron diffraction, we show that the twin reorientation under a magnetic field is described by thermally-activated creep motion over a distribution of energy barriers. The dynamical creep exponent μ was found to be ~ 0.5, suggesting that the energy distribution is due to shortrange disorders.