Improvement of soft magnetic properties for Fe-based amorphous/nanocrystalline alloy by longitudinal magnetic field annealing

This study investigated the enhancement of soft magnetic properties in Fe_83.2-xCo_xSi_2.5B_9.5P₄Cu_0.8 (x = 0, 4, 8, 12 and 16 at %) amorphous/nanocrystalline alloys through longitudinal magnetic field annealing (FA). The FA-treated alloys demonstrate superior magnetic performance, achieving a superior saturation flux density (B_s) of 1.85 T, ultra-low coercivity (H_c) of 1.8 A/m, high effective permeability (μ_e) of 26,505 at 1 kHz, and low core loss (0.13 W/kg) at 1.0 T/50 Hz. Microstructural analysis reveals that the FA and Co substitution promotes nanocrystalline nucleation, forming high-density nanocrystals while suppressing grain growth through competitive dynamics and inhibiting element diffusion within the amorphous matrix. Domain observation further confirms that FA facilitates the transition from disordered, non-uniform magnetic to uniform, broad, plate-like domains. These findings elucidate the critical influence of longitudinal magnetic field annealing on microstructure evolution and magnetic domain alignment, which synergistically enhance soft magnetic properties.