Magnetic properties and structure of Fe83.3–85.8B7.0–4.5P9Cu0.7 nanocrystalline alloys

The effects of Fe content on the magnetic properties and fine structure of the nanocrystalline Fe-B-P-Cu alloys have been investigated, with the objective of enhancing their magnetic softness. The nanocrystalline Fe83.3+xB7−xP9Cu0.7 (x = 0.0–2.5) alloys annealed at 673 K consist of uniform α-Fe grains embedded in a residual amorphous phase, and the average α-Fe grain diameter decreases from 18.1 to 14.6 nm with increasing Fe content. At the same time, the saturation magnetic flux density (Bs) increases and the coercivity (Hc) decreases with increasing Fe content and the x = 1.0 alloy has a high Bs of 1.72 T and a low Hc of 2.9 A/m. At x = 2.0 or higher, however, Hc drastically deteriorates from the effect of the coarse α-Fe grains. The core loss (W) of the x = 1.0 alloy at 50 Hz-1.6 T is 0.26 W/kg, which is one-third of that for oriented magnetic steel. These results indicate that the magnetic properties and structure of nanocrystalline Fe-B-P-Cu alloys are strongly affected by Fe content.