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

Abstract 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) Fe 35 Co 35 Al 10 Cr 10 Ni 10 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.