Effect of heating rate on atom migration, phase structure and magnetic properties of the Fe82Si2B11P4Cu1 alloy

Atom migration, phase structure and magnetic properties in the Fe82Si2B11P4Cu1 amorphous alloy isothermally annealed at various heating rates are investigated. Annealing the samples at a high heating rate promotes the formation of Cu-rich regions and delays the phase separation process to high temperature, which is conductive to increase the volume fraction of the nanocrystalline phase and refine nanograins during the crystallization. When the alloy is isothermally annealed at 758 K for 180 s, the saturation magnetic flux density increases from 1.74 T to 1.79 T and the coercivity decreases from 7.8 A/m to 4.4 A/m with the heating rate increasing from 0.5 K/s to 20 K/s. Meanwhile, it confirms that the occupation of Si atoms in the lattice of bcc-Fe can be suppressed by the annealing with high heating rate. Increasing the heating rate is widely regarded as an effective method to improve soft magnetic properties of Fe-based nanocrystalline alloys. However, it is found that the content of the nonmagnetic atom enriched regions rises with the increase of heating rate, which can reduce the magnetic interaction in the nanocrystalline ribbons. Therefore, the exorbitant heating rate reaching 40 K/s will dramatically promote the aggregation of nonmagnetic atoms and deteriorate the soft magnetic properties.