Magnetic field-induced rubber-like behavior in Ni-Mn-Ga particles/polymer composite.

Single crystalline Ni-Mn-Ga is well known as a prototype ferromagnetic shape memory alloy (FSMA) exhibiting a giant magnetic field-induced strain (MFIS), up to 12%, due to the magnetically driven twin boundary rearrangement. The large stroke and fast magnetomechanical response make it important for actuators and sensors. Polycrystalline Ni-Mn-Ga is inexpensive and technologically easy accessible, but constrains from the grain boundaries inhibit the twin boundary motion, whereby a very low MFIS is observed. Here, we have shown for the first time that a polycrystalline Ni-Mn-Ga can be split into the magnetostrain-active single grains which, being specially assembled in a silicone polymer matrix, caused large and fully reversible MFIS of the resulting composite. We termed the unique reversibility of a large MFIS of the composite as the magnetic field-induced rubber-like behavior. The magnetostrain of individual particles was explored by the X-ray μCT 3D imaging. The results suggest novel solutions for development of the low cost magnetic actuators and sensors for haptic applications.