Microalloying and pre‐annealing co‐modulation of the nanocrystalline structure and soft magnetic properties of Fe(Co)SiBPCu alloys

Abstract Elemental modulation and heat treatment optimization have emerged as pivotal strategies for enhancing the soft magnetic properties of alloys. We thoroughly examine the impact of microalloyed Co on the amorphous formation ability, thermal stability, and soft magnetic properties of Fe 80 Co x Si 7‐ x B 8 P 4 Cu 1 ( x = 0, 0.5, 1, 1.5, 2) alloys. The influence of different annealing processes on these properties is analyzed through detailed insights into the evolution of nanocrystalline microstructure and magnetic domain behavior. Our findings indicate that Co addition facilitates the nucleation and growth of the α‐Fe (Si, Co) phase while broadening the thermal processing window, thereby significantly improving the alloy’s soft magnetic properties. Notably, the alloy with x = 1 undergoes a pre‐annealing and reheating process to yield a finer, denser, and more uniform nanocrystalline structure (average grain size D = 20.29 nm, grain density N d = 1.5 × 10 23 m −3 ). This refinement enables the formation of broad magnetic domains characterized by 180° domain walls, culminating in exceptional soft magnetic properties, including a high magnetic flux density ( B s = 1.81 T), high effective permeability ( μ e = 18,014), and low coercivity ( H c = 5.57 A m −1 ). Further, the pinning fields ( H p ) for the x = 1 alloy are notably low, ranging from 15 to 20 A m −1 , while the maximum effective permeability reaches 69,300. These exceptional properties are directly linked to the alloy’s minimized total free energy ( E ) and its highly homogeneous microstructure, which collectively suppress magnetic pinning effects. Such characteristics position the x = 1 alloy as an exceptional candidate for high‐sensitivity applications, particularly in sensor device systems functioning under mild magnetic fields and necessitating swift reaction.