Giant magnetostrains in MnFe(P,Si,B)/epoxy composites at intermediate magnetic fields

Magnetostrictive materials are widely used in actuators, sensors, and energy-harvesting systems, but many high-performance compounds rely on heavy rare-earth elements or require high magnetic fields to develop giant magnetostrains. Here, we present Fe₂P/epoxy composites, exploiting an anisotropic first-order ferromagnetic transition (FOMT) to generate giant magnetostrains. A parametric model based on structural discontinuities and thermodynamic considerations is proposed to guide composition selection. Textured MnFe_0.95P_0.55Si_0.40B_0.05/epoxy composites were prepared by magnetic field alignment and characterized by strain-gauge dilatometry measurements as a function of temperature and magnetic field. Near the FOMT, despite matrix dilution effects, linear magnetostrains up to 0.22% at 2 T (0.37% at 7 T) are achieved. In particular, at intermediate fields, the magnetostrain shows a nearly linear increase with the field of about 0.1%/T (1000 ppm/T) with limited hysteresis. These results demonstrate that Fe₂P-type compounds, previously developed for magnetocaloric applications, can be adapted into scalable, low-cost magnetostrictive composites with tunable transition temperatures that rely only on abundant elements.