Reversible Magnetic Field Induced Strain in Ni₂MnGa‐Polymer‐Composites

Abstract Composite materials consisting of magnetic shape memory alloy particles and a polymer matrix combine the advantages of both material classes: the high achievable magnetic field induced strain (MFIS) of 6% of Ni‐Mn‐Ga with a ductile matrix. Engineering the particle‐matrix interface as well as matching stiffness of polymer matrix is of importance for achieving high reversible MFIS to use this material as actuator or damper. We investigated those properties for Ni_50.9Mn_27.1Ga_22.0 and Ni_50.3Mn_24.6Ga_25.1 polymer composites. Particles were produced by gently crushing melt‐extracted and subsequently annealed fibres. At room temperature, the Ni_50.9Mn_27.1Ga_22.0 particles exhibit a 5M martensitic structure, while the Ni_50.3Mn_24.6Ga_25.1 particles are austenitic. These particles were embedded into the polymer, either a stiff epoxy resin or a soft polyurethane. In response to an external applied magnetic field, the particles tend to relocate within the polyurethane due to its very low Young's modulus and magnetostatic interaction between particles. Slightly stiffer polymer matrices are advantageous for achieving controllable MFIS. In Ni_50.9Mn_27.1Ga_22.0 epoxy composites, a MFIS of 0.1% was observed and was resettable by rotating the magnetic field by 90°. Furthermore, single fibre pull‐out tests indicated significant improvements of the interfacial properties when using silane coupling agent treated fibres.