Engineering Magnetic Interactions to Achieve Low-Field Actuation in Ni–Mn–Ga Single-Crystalline Particle Composites

Single-crystalline (SC) Ni-Mn-Ga particles/silicone rubber composites exhibiting large magnetic field-induced strain (MFIS) are promising candidates for high-speed actuator applications. Nevertheless, a key challenge for practical use is lowering the magnetic field (H-field) required to activate shape deformation. To achieve this, soft magnetic Fe- and FeNi-added SC Ni-Mn-Ga particles/silicone composites have been developed; however, the investigations of the magnetic property and the dimensional issues are not well discussed. In this study, Fe-Si-Al (Sendust) particles were introduced into SC Ni-Mn-Ga particles/silicone rubber composites to investigate their influence on MFIS behavior of the composite. Sendust particles possess a higher initial magnetic permeability and larger particle dimensions compared to Fe and FeNi particles used in previous studies. The magnetic, mechanical, and MFIS behaviors of four composites containing Sendust and/or SC Ni-Mn-Ga particles fabricated under different curing conditions were examined. The results show that tailoring Sendust particles decreased the necessary H-field for the commencement of shape deformation. A comparison of MFIS behavior among Fe-, FeNi-, and Sendust-tailored composites revealed that higher magnetization and larger dimensions could be advantageous for enhancing MFIS response. Furthermore, magnetic finite element simulations were conducted to elucidate the roles of magnetic properties and particle dimensions of tailoring materials in governing magnetic interactions with Ni-Mn-Ga particles. These results indicate that tailoring materials with higher magnetization and larger particle dimensions effectively reduce the necessary H-field for actuation. These findings provide design guidelines for advanced smart composites.