Three-dimensional atom probe study of Fe–B-based nanocrystalline soft magnetic materials

Solute clustering and partitioning in new Fe–B-based soft magnetic materials with high saturation magnetic flux density (Bs), (Fe0.85B0.15)100−xCux (x = 0.0, 1.0, and 1.5) and Fe82.65Cu1.35SiyB16−y (y = 0.0, 2.0, and 5.0) melt-spun alloys, were investigated by three-dimensional atom probe and transmission electron microscopy. Although Cu clusters form after annealing in all the samples, it was found that only the clusters of 4–6 nm can serve as heterogeneous nucleation sites for α-Fe. While annealing the Si-free alloys at 410 °C led to the precipitation of Fe3B, only α-Fe nanocrystals were observed in the Si-containing alloys. Lorenz TEM observation indicated the Fe3B particles pin magnetic domain walls. The Fe82.65Cu1.35SiyB16−y alloy with y = 2.0 crystallized by annealing at 400 °C exhibited optimal nanocrsytal/amorphous microstructure without the precipitation of Fe3B, which led to the lowest coercivity while keeping a high Bs ∼1.85 T.