Near-zero magnetostriction in magnetostrictive FeCo alloys

Soft magnetic metallic materials are the key components in generators, motors and transformers. The Curie temperatures of currently used soft magnetic metallic materials limit their applications in high-temperature environments. In this work, we tuned the bcc/fcc ratio through modifying the Co content, thus obtaining near-zero magnetostriction and improved soft magnetic properties in the magnetostrictive system Fe_100-xCo_x (70≤x≤93) alloys with high Curie temperature. With the increase of Co content, we observed the evolution of three crystal structures from bcc to fcc and three types of magnetostriction curves, ∧-type, ∨-type and M-type, which can be well interpreted by the domain-switching model. The optimum composition Fe₂₀Co₈₀, corresponding to the coexistence of bcc & fcc phases, exhibits magnetostriction of -3 ppm, a coercive field of 0.18 kA/m and saturated magnetization of 183 Am²kg⁻¹. Our study provides an effective route to design magnetic functional materials with zero magnetostriction.