Design of Tunable Magnetization Response in CuFeCo Immiscible Alloys via Directional Solidification

Soft magnetic materials with tunable magnetization response are urgently needed for next-generation adaptive electromagnetic devices, yet conventional alloys face inherent limitations in balancing high saturation magnetization (M_s) and controllable magnetic sensitivity. Here, we propose CuFeCo immiscible alloys fabricated via directional solidification to overcome this challenge. By introducing immiscible Cu-rich phase into the FeCo-rich matrix, coupled with controlled pulling speeds (10-200 μm/s), we achieve simultaneous enhancement of M_s and precise adjustment of the slope of the magnetization curve (dM/dH). The resulting alloy exhibits an exceptional M_s of 160.7 emu/g (at 200 μm/s), while enabling a wide-range dM/dH adjustment from 38 to 83 kA/(m·T). Our analysis reveals that changes in the directional solidification pulling speed induce a transition in the solidification microstructure from cellular dendrites to fibrous dendrites. A Cu-rich zone exists between FeCo-rich dendrites, and as the dendrites become progressively refined, the FeCo-rich phase fraction increases, leading to an enhancement in M_s. The <001> texture volume fraction of the FeCo-rich phase, dominated by preferential growth competition, increased from 32% to 57%, contributing to the enhancement of dM/dH. Magnetocrystalline anisotropy induces differential magnetization rates between the parallel and perpendicular orientations in the microstructure. Additionally, coercivity (H_c) exhibits an initial increase followed by a subsequent decrease, as FeCo-rich/Cu-rich phase boundaries gradually replace FeCo-rich dendrites grain boundaries, making the strip-like domains more continuous. Our work establishes a paradigm for designing property-programmable soft magnetic materials, bridging the gap in adaptive electromagnetic functionality.