Magnetostrain behavior of particle grid in particulate Ni–Mn–Ga(Fe)/silicone rubber composites

Composite materials made of Ni-Mn-Ga particles and silicone polymer, which exhibit large magnetic field induced strain (MFIS), good cyclic and long-term stabilities, are highly promising for use in actuation and sensing applications. Whereas MFIS of these composites and their individual particles has been thoroughly investigated in our previous research, MFIS of the ensemble of particles, which are crystallographically and spatially aligned in composite samples, known as the particle grid, has not yet been explored. Since MFIS of a particle grid determines the magnetic field induced shape change of the entire composite, it was crucial to determine how the variation in the spatial dimensions of the grid affects the overall shape change of the composite. In this study, we examined the magnetization curves and magnetostrain behavior of particle grids in six composites, with different fillers such as Ni-Mn-Ga and Fe particles, produced through distinct manufacturing schemes. We used a standard vibrating sample magnetometer and an innovative method that utilized X-ray microCT 3D imaging. It was found that applying a magnetic field perpendicularly to the particle chains causes large strains along the main directions of the particle grid, which differ in magnitude from those observed for composites as a whole known from the literature. Both the effect of peculiar MFIS transfer from particles grid to the entire composite and the impact of Fe particles are examined in relation to the spatial distribution of the particles and their interaction with the polymer matrix.