Rapid actuation and response of Ni-Mn-Ga to magnetic-field-induced stress

The mechanism that is responsible for the large strains in the magnetic shape memory (MSM) alloy Ni-Mn-Ga is the movement of twin boundaries caused by an internal magnetic-field-induced stress. This is the primary property that makes Ni-Mn-Ga such an attractive material for use as an actuator. Hence, a deeper understanding of the movement and dynamics of twin boundaries in Ni-Mn-Ga would enable the development of applications that could take full advantage of the material's properties. In this study, a novel experimental method was developed that could observe, in situ, the movement of a single twin boundary within a sample of Ni-Mn-Ga. A twin boundary velocity of 82.5 m s^-1, an actuation response time of 2.8 μs and an actuation acceleration of 1.6 × 10⁶ m s^-2 were experimentally observed. These experimental results have also been validated by an independently developed theoretical model. This is the most rapid actuation and twin boundary movement of all actuating materials on this scale and these results may have a significant impact on future applications, particularly in microtechnology where speed and precision are essential.