Structural Modulation of Magnetic Softness in Fe-Based Amorphous Alloys via Pulse Current Training

Fe-based amorphous alloys, despite their intrinsically low magnetocrystalline anisotropy, suffer from quasi-dislocation dipoles and localized stress fields that impede domain-wall motion and increase coercivity. Here, we introduce pulse current training (PCT) as an energy-efficient technique to overcome these limitations in a Fe₇₆Si₉B₁₀P₅ ribbon. As quenched ribbons exhibit a coercivity H_c ∼ 10.6 A m⁻¹ and the optimized infrared annealing reduced H_c ∼ 2 A m⁻¹ with a saturation magnetization M_s ∼ 162 emu g⁻¹. By applying controlled square-wave current pulses (J = 7000 A cm⁻², T_w:T_p = 1:2, T_p = 0.06 s) over 18–50 cycles, PCT further reduces H_c to below 1 A m⁻¹ and increases M_s to 179 emu g⁻¹. Within a moderate-cycle window, the ribbons maintain sufficient bendability for a practical core. Ultra-rapid thermal annealing performed as a control reduces H_c to ∼2.5 A m⁻¹ but does not reach the level achieved by PCT, indicating that rapid heating alone cannot account for the superior magnetic softening. Finite-element simulations and structural characterization show that PCT produces rapid and nearly uniform Joule heating, enabling efficient structural relaxation and enhanced medium-range order while retaining an overall amorphous structure. Compared with conventional annealing, PCT implements a distinct, pulse energy injection pathway on the potential energy landscape, enabling more controllable tuning of amorphous configurations. This work establishes PCT as a versatile approach for tailoring both magnetic and mechanical properties in amorphous soft magnetic materials, paving the way for their optimized application in advanced electromagnetic devices.