Synthesis of Fe16N2 compound Free-Standing Foils with 20 MGOe Magnetic Energy Product by Nitrogen Ion-Implantation.

Yanfeng Jiang,Lawrence F Allard,Md Al Mehedi,Jian-Ping Wang,Engang Fu,Yongqiang Wang

doi:10.1038/srep25436

Abstract

Rare-earth-free magnets are highly demanded by clean and renewable energy industries because of the supply constraints and environmental issues. A promising permanent magnet should possess high remanent magnetic flux density (Br), large coercivity (Hc) and hence large maximum magnetic energy product ((BH)max). Fe16N2 has been emerging as one of promising candidates because of the redundancy of Fe and N on the earth, its large magnetocrystalline anisotropy (Ku > 1.0 × 107 erg/cc), and large saturation magnetization (4πMs > 2.4 T). However, there is no report on the formation of Fe16N2 magnet with high Br and large Hc in bulk format before. In this paper, we successfully synthesize free-standing Fe16N2 foils with a coercivity of up to 1910 Oe and a magnetic energy product of up to 20 MGOe at room temperature. Nitrogen ion implantation is used as an alternative nitriding approach with the benefit of tunable implantation energy and fluence. An integrated synthesis technique is developed, including a direct foil-substrate bonding step, an ion implantation step and a two-step post-annealing process. With the tunable capability of the ion implantation fluence and energy, a microstructure with grain size 25–30 nm is constructed on the FeN foil sample with the implantation fluence of 5 × 1017/cm2.

Highlights

Rare-earth-free magnets are highly demanded by clean and renewable energy industries because of the supply constraints and environmental issues of rare-earth permanent magnets in recent years[1]
The characterization is conducted in the foil plane using a Vibrating Sample Magnetometer (VSM) calibrated by a standard Ni sample at room temperature
Its remanent magnetization value is equal to its saturation magnetization value, which is around 206 emu/g at room temperature

Summary

Introduction

Rare-earth-free magnets are highly demanded by clean and renewable energy industries because of the supply constraints and environmental issues of rare-earth permanent magnets in recent years[1]. Nitriding, strain and microstructure are the three important aspects of Fe16N2 permanent magnet preparation. No approach is reported to prepare Fe16N2 bulk samples, which could optimize all these three key aspects, including nitriding, strain and microstructure, at the same time. Soft magnetic property on larger particles, hard magnetic property on small particle (< 50 nm) contradiction means the microstructure of α-Fe16N2 can’t be directly tuned by traditional annealing method This is why, until now, there isn’t any report on how to tune the microstructure on α-Fe16N2 bulk sample yet. To prepare an α-Fe16N2 permanent magnet in bulk format, it is strategically important to investigate one synthesis technique, by which nitriding, strain and microstructure engineering could be all taken into consideration

Results

Discussion

Conclusion