Development of Bonded $\boldsymbol{\alpha}^{\prime \prime}-\mathbf{Fe}_{\mathbf{16}} \mathbf{N}_\mathbf{2}$ Permanent Magnet

Because of their great technological impacts, permanent magnets play a crucial role in various aspects of modern life [1]–[2]. The problems generated by the availability and the resulting pollution to obtain the rare earths used in the preparation of the current permanent magnets stimulated intense research for the development of alternative materials. The iron nitride materials, especially $\alpha^{\prime\prime}\text{-Fe}_{16}\mathrm{N}_{2}$, are considered one of the most promising candidates for future rare earth free semi-hard magnetic materials [3] since they possess a giant saturation magnetization of ~2.9 T (~305 emu/g) [4]–[5] and the constituent materials Fe and N are abundant and environmentally friendly [6]. So far, many efforts have been made both on the fundamental [7]–[8] and experimental aspects of the preparation of the $\alpha^{\prime\prime}-\text{Fe}_{16}\mathrm{N}_{2}$ material in various forms such as thin layers, strips, nanopowders [9]–[12]. However, the preparation of permanent magnets based on $\alpha^{\prime\prime}\text{-Fe}_{16}\mathrm{N}_{2}$ is still challenging. Current production of dense permanent magnets consists of powder production, pressing and magnetic field alignment, sintering, and post-processing. But the $\alpha^{\prime\prime}\text{-Fe}_{16}\mathrm{N}_{2}$ powders are considered difficult to compact by sintering techniques that are commonly used for bulk magnets because the $\alpha^{\prime\prime}\text{-phase}$ decomposes at temperatures higher than 200°C. In addition, it was reported that ultra-high pressure compaction above 5 GPa led to partial decomposition of the $\alpha^{\prime\prime}$ phase transition into $\gamma^{\prime}\text{-Fe}_{4}\mathrm{N}$ and $\gamma^{\prime\prime}-\text{FeN}$ phases [13]. Consequently, due to the critical thermo-mechanical instability of the $\alpha^{\prime\prime}- \text{Fe}_{16}\mathrm{N}_{2}$ phase, here we propose the preparation of $\alpha^{\prime\prime}\text{-Fe}_{16}\mathrm{N}_{2}$ magnets employing a bonding method at the expense of magnetic performance due the mixing with non-magnetic polymer.