Optimizing the soft magnetic behavior of iron nitride*

The γ’ phase of iron nitride holds tremendous potential as a new soft magnetic material with a saturation magnetic polarization of 1.89 T and a high electrical resistivity (> 20,000 µΩcm) capable of mitigating eddy current losses. However, until recently γ’–Fe₄N had only been synthesized and studied as a thin film, making the fabrication of devices such as inductive cores impossible. New low temperature consolidation techniques, such as spark plasma sintering (SPS), have enabled the fabrication of bulk γ’–Fe₄N samples and devices while avoiding thermal decomposition. Although the synthesis of bulk γ’–Fe₄N was a significant achievement, efforts are continuing to enhance its soft magnetic properties by improving phase purity and controlling grain size, while further increasing electrical resistivity. These efforts, which include advances in the synthesis of raw materials, processing techniques, and composite approaches will be described.