Fabrication and magnetic characterization of phosphate-coated iron–cobalt soft magnetic composites

Soft magnetic composites (SMCs) have gained interest for applications associated with passive electronics and motor components due to their low total core losses and affordability. However, a need has arisen for SMCs that can operate at high frequencies with high magnetizations, leading to a search for novel materials that can breach these frequency thresholds while maintaining a high saturation magnetic polarization ( J s ) without ceding to core losses. Specifically, the iron–cobalt alloy exhibits a high J s value, but possesses a low resistivity ( ρ ), impeding its integration into electric motors and machinery. However, by employing an insulating layer, the resistivity of the material can be increased. Seeking a facile synthesis to bolster the resistivity of FeCo SMCs, we investigated an insulating phosphate coating at two weight percents: 0.1 and 0.2 wt%. With the 0.2 wt% SMCs, the ρ values exceeded 1.0E05 μΩ-m and achieved an average J s value of 2.1 T, while the 0.1 wt% SMCs maintained comparable J s values but exhibited a resistivity below 100 μΩ-m. In addition to the phosphate coating weight percent, the annealing temperatures also impacted the magnetic properties as well as the structural integrity of the samples. This allowed for pressing of a variety of sample shapes such as cylinders, tiles, bricks, and toroids. Additionally, encasing pure metal powder toroids in epoxy coating and fabricating epoxy/powder composite toroids provided two methods for improving their robustness. Progress was made in the effort to find soft magnetic materials that result in the ideal balance between size, weight, and power of electric motor/machinery components.