Speakers

​​​​​​​​​​​​​​​​​Ni–Mn–Ga ferromagnetic shape memory alloys (FSMAs) are well known for their giant magnetic field-induced strain (MFIS), fast response, and high energy conversion capability, making them promising candidates for advanced actuator and sensor applications. However, their intrinsic brittleness and high fabrication cost in bulk form limit practical applications. To address these challenges, composite and laminate systems incorporating Ni–Mn–Ga particles have emerged as a versatile and cost-effective alternative, offering enhanced mechanical robustness and design flexibility.​

In this study, we systematically investigate the magnetization and magnetostrain behaviors of Ni–Mn–Ga-based composites and laminate structures, with particular emphasis on particle interactions, microstructural design, and magneto-mechanical coupling. For particle/silicone composites, we explore the role of particle alignment and spatial organization, specifically focusing on particle grid architectures.

In bulk composites, using vibrating sample magnetometry and X-ray micro-computed tomography (µ-CT), we reveal that magnetostrain strongly depends on the collective behavior of crystallographically aligned particle ensembles rather than individual particles. The application of magnetic fields perpendicular to particle chains induces significant anisotropic strain, highlighting the importance of spatial distribution and inter-particle interactions. Furthermore, we introduce soft magnetic fillers, such as Fe and FeNi particles, to enhance magnetic responsiveness. The incorporation of high-permeability materials leads to a steeper magnetostrain–magnetic field response and enables large strains at lower magnetic fields, which is advantageous for low-energy actuation systems. Additionally, the influence of mechanical constraints, such as compression cycling and in-situ opposing stress, is examined. The results demonstrate a substantial reduction in the switching magnetic field and a narrowing of the reorientation interval due to stress-induced effects, including barreling deformation.

In laminate composites consisting of single-crystalline Ni–Mn–Ga particles sandwiched between metallic foils, replacing non-magnetic Cu with soft magnetic Fe foils significantly reduces the threshold field required for martensitic variant reorientation. This effect is attributed to additional tensile stress generated by magnetically induced repulsive forces between Fe layers. Quantitative analysis further reveals a magnetic-to-mechanical energy conversion coefficient comparable to that of bulk single crystals.

These findings provide new insights into the design of FSMA-based composites and laminates, demonstrating that microstructural engineering and the integration of soft magnetic components are effective strategies for enhancing MFIS performance. This work paves the way for the development of high-efficiency, miniaturized actuators and sensing devices.