Co-based Heusler alloys have emerged as highly promising systems within the Heusler alloy family due to their high Curie temperatures and potential half-metallicity. Since the concept of half-metallic ferromagnets was proposed, these alloys have attracted significant attention for their high spin polarization, excellent magnetic performance, and thermal stability. However, while existing studies predominantly focus on spin-transport properties, systematic studies on their magnetostriction remain scarce. The electronic structure and magnetism of Co-based Heusler alloys are critically dependent on atomic-site ordering: their spin polarization, Curie temperature, and magnetocrystalline anisotropy are closely correlated with crystal structures (e.g., L2₁, B2). A highly ordered L2₁ structure is essential for preserving half-metallicity, whereas structural disorder can induce significant changes in electronic hybridization and exchange interactions, which significantly alter macroscopic magnetic properties. Additionally, ordering control is also expected to modulate magnetostriction by modifying lattice symmetry and local distortions. Notably, in Fe–Ga alloys, disorder engineering has been employed to induce local short-range order and lattice distortions, thereby enhancing magnetostriction—a mechanism that may similarly operate in Co-based systems. However, the higher lattice symmetry and stronger orbital hybridization in these alloys could lead to fundamentally distinct mechanisms requiring experimental validation. In this study, we focus on the Co₂FeAl_xSi_1-x system to systematically probe the relationship between composition-driven structural evolution (i.e., L2₁ to B2 transition) and magnetostrictive performance via Al/Si ratio tuning. The study aims to clarify the correlation between composition-induced structural evolution and magnetostrictive behavior, thereby revealing the regulatory role of atomic ordering in magnetoelastic coupling and providing theoretical insight for the design of high-performance magnetostrictive materials.
This study systematically investigates the correlation between atomic site ordering and magnetostriction in the Heusler alloy Co₂FeAl_xSi_1-x (x = 0, 0.25, 0.5, 0.75, 1) through experimental methods. The results reveal that Al doping drives a structural transition from the highly ordered L2₁ phase to the disordered B2 phase, inducing a coexisting L2₁/B2 interface state at x = 0.25~0.5, where the calculated ordering parameters S_L21/S_B2 range from 0.5 to 0.9. The experimental data demonstrate that this interface state significantly enhances the saturation magnetostriction coefficient (λ_s), which subsequently decreases upon further transition to the B2-dominated structure. These findings quantitatively clarify the physical mechanism by which local atomic disorder enhances magnetoelastic coupling through reduced cubic symmetry, localized lattice distortions, and altered magnetic domain configurations. Furthermore, this work first reports the magnetostriction coefficients of 12 Co-based Heusler alloys, among which Co₂MnGa and Co₂CrGa exhibit superior potential compared to others, filling the gap in performance parameters for this system. The linear positive magnetostriction behavior of the polycrystalline materials is also validated. This study proposes a strategy for optimizing magnetostriction performance through atomic site ordering control, offering a new direction for the development of magnetostrictive materials with high-temperature stability and high spin polarization.