Magnetic properties and structure of Fe_83.3-85.8B _7.0-4.5P₉Cu_0.7 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 Fe _83.3xB_7-xP₉Cu_0.7 (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 (B_s) increases and the coercivity (H_c) decreases with increasing Fe content and the x 1.0 alloy has a high B _s of 1.72 T and a low H_c of 2.9 A/m. At x 2.0 or higher, however, H_c 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.