Recent progress in research and development of rare-earth free iron nitride permanent magnet

Abstract

The high cost of rare earth materials, unstable supply and high demand remain big problems to solve for permanent magnet industries. Thus α″-Fe<sub>16</sub>N<sub>2</sub> has been picked up as one of the most promising rare earth-free magnet candidates because of its use of environmental-friendly raw materials, confirmed giant saturation magnetic flux density (2.9 T), and reasonably high magnetic anisotropy constant (1.8 MJ/m<sup>3</sup>). Also, α”-Fe<sub>16</sub>N<sub>2</sub> metastable with film form exhibits high tetragonality (c/a=1.1) by interstitial introduction of N atoms, leading to a high magnetocrystalline anisotropy constant (K<sub>u</sub> = 1.0 MJ/m<sup>3</sup>). but synthesis of bulk form has lower properties than thin film (<230 nm) because of magnetic interaction, experimentally low anisotropy, and low density. In this paper, we review the synthetic methods of metastable α”-Fe<sub>16</sub>N<sub>2</sub> with powder and bulk form and discuss the approaches to enhance magnetocrystalline anisotropy of α”-Fe<sub>16</sub>N<sub>2</sub>.