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.

Mn compounds presenting magneto-structural phase transitions are currently intensively studied for their giant magnetocaloric effect; nevertheless, several parameters remain to be further optimized. Here, we explore the Mn(Fe,Ni)(Si,Al) series, which presents two advantages. The Mn content is fixed to unity ensuring a large saturation magnetization, and it is based on non-critical Si and Al elements instead of the more commonly employed Ge. Structural and magnetic properties of MnFe_0.6 Ni_0.4 Si_1-x Al_x compounds are investigated using powder X-ray diffraction, SEM, EDX, DSC, and magnetic measurements. We demonstrate that a magneto-structural coupling leading to transformation from ferromagnetic with orthorhombic TiNiSi-type structure to a paramagnetic hexagonal Ni₂ In-type phase can be realized for 0.06 < x ≤ 0.08. Unfortunately, the first-order transition is relatively broad and incomplete, likely as the result of insufficient sample homogeneity. A comparison between samples synthesized in different conditions (as-cast, quenched from 900^◦ C, or quenched from 1100^◦ C) reveals that Mn(Fe,Ni)(Si,Al) samples decompose into a Mn₅ Si₃-type phase at intermediate temperatures, preventing the synthesis of high-quality samples by conventional methods such as arc-melting followed by solid-state reaction. By identifying promising MnFe_0.6 Ni_0.4 Si_1-x Al_x compositions, this study paves the way toward the realization of a giant magnetocaloric effect in these compounds using alternative synthesis techniques.