A constrained theory on actuation strain in ferromagnetic shape memory alloys induced by domain switching

A constrained theory of magnetoelastic materials is applied to study the ferromagnetic shape memory effect in single crystals and polycrystals. The actuation strain induced by domain switching is established first for ferromagnetic shape memory single crystals, from which the strain in polycrystals is derived using Taylor estimate. Both NiMnGa and FePd are analyzed, and the necessary fiber texture for large actuation strain in tetragonal polycrystals is identified. For orthorhombic polycrystals, such a fiber texture is not required. The analysis agrees with experimental observations well.