Fe16N2: from a 40-year mystery of magnetic materials to one of promises for rare-earth-free magnets

Fe
16
N
2
is one of the most promising rare-earth-free magnet candidates with high magnetic energy product. Iron nitride magnet is of great interest as a magnetic material for applications at relatively low temperature $( \lt 150\,\,{}^{\circ}\mathrm {C})$ ranging from magnets in hard disk drives for data storage and in all kinds of electrical motors, wind turbines, and other power generation machines. A perspective review on our research work on bulk Fe
16
N
2
compound permanent magnet in past years is presented on the aspects of material processing and magnetic characterizations. Specifically, we will introduce and discuss our effort to prepare bulk Fe
16
N
2
compound permanent magnet by using three different approaches, including an ion implantation method, a ball milling method and a strained-wire method. A feasibility of free-standing iron nitride foils with magnetic energy product up to 20 MGOe was successfully demonstrated based on an ion implantation method. Based on our theoretical and experimental progress, we believe that Fe
16
N
2
compound permanent magnet is currently in an accelerating step to be an alternative magnet candidate.