Large Nonhysteretic Volume Magnetostriction in a Strong and Ductile High‐Entropy Alloy

Rapid development of smart technologies poses a big challenge for magnetostrictive materials, which should not only permit isotropic and hysteresis-free actuation (i.e., nonhysteretic volume change) in magnetic fields, but also have high strength and high ductility. Unfortunately, the magnetostriction from self-assembly of ferromagnetic domains is volume-conserving; the volume magnetostriction from field-induced first-order phase transition has large intrinsic hysteresis; and most prototype magnetostrictive materials are intrinsically brittle. Here, a magnetic high-entropy alloy (HEA) Fe₃₅Co₃₅Al₁₀Cr₁₀Ni₁₀ is reported that can rectify these challenges, exhibiting an unprecedented combination of large nonhysteretic volume magnetostriction, high tensile strength and large elongation strain, over a wide working temperature range from room temperature down to 100 K. Its exceptional properties stem from a dual-phase microstructure, where the face-centered cubic (FCC) matrix phase with nanoscale compositional and structural fluctuations can enable a magnetic-field-induced transition from low-spin small-volume state to high-spin large-volume state, and the ordered body-centered cubic (BCC) B2 phase contributes to mechanical strengthening. The present findings may provide insights into designing unconventional and technologically important magnetostrictive materials.