Pramanand Joshi / Physics / Faculty Mentor: J. Ping Liu
Rare-earth elements, which are critical for the production of permanent magnets, face supply chain challenges due to their limited availability. In this study, we present rare-earth-free Hagg carbide (Fe₅C₂) nanocrystals with spherical and rod-shaped morphologies, demonstrating a record-high coercive field of 1.6 kOe and a saturation magnetization of ~122 emu/g at room temperature. These nanocrystals exhibit a Curie temperature of 520 K, making them highly suitable for permanent magnet applications. We modulated their aspect ratios from 1 to 3, achieving enhanced anisotropy. For the rod-shaped sample (aspect ratio of 3), we observed the highest coercivity, with a hysteresis loop along the alignment direction showing a coercivity of 1.6 kOe and squareness of 0.82. As the aspect ratio decreased, coercivity along the alignment direction also decreased, and the parallel and perpendicular hysteresis loops became more similar, indicating successful tuning of anisotropy in the Fe₅C₂ nanocrystals. Additionally, the temperature dependence of coercivity aligns well with the Kneller law, providing a blocking temperature (507 K, for a sample) which closely matches the value observed in the zero-field cooling/field cooling (ZFC-FC) measurement.
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