Preparation of an α″‐Fe₁₆N₂ Magnet via a Ball Milling and Shock Compaction Approach

Abstract

a 00 -Fe 16 N 2 has been suggested as a promising candidate for future rare-earth-free magnets. In this paper, a unique technical route including a ball milling approach and shock compaction is experimentally demonstrated as a promising way to produce an a 00 -Fe 16 N 2 magnet. Firstly, a 00 -Fe 16 N 2 powder is prepared by ball milling, in which ammonium nitrate (NH 4 NO 3 ) is adopted as a solid nitrogen source. The volume ratio of the a 00 -Fe 16 N 2 phase reaches 70% after 60 h of milling with a ball mill rotation speed of 600 rpm in planetary mode. Its saturation magnetization (M s ) is 210 emu g -1 and the coercivity is 854 Oe at room temperature. After ball milling, shock compaction is used to compact the milled powder sample into a bulk magnet. Its magnetic properties and crystalline structure are characterized. Overall, the ball milling-based approach can be used to prepare a 00 -Fe 16 N 2 magnets at an industrial production level.

Fabrication and Characterization of Fe16N2Micro‐Flake Powders and Their Extrusion‐Based 3D Printing into Permanent Magnet Form

“…the usual permanent magnet production routes, involving treatment at high temperature, [1] cannot be used. To circumvent these difficulties, several methods have been used, including shock compaction of nanoparticles, [21] strained wire method, [18] and resin bonding of individual ribbons. [20] Most recently, Liu et al [28] synthesized the prototype bonded magnet of Fe 16 N 2 by stacking low-temperature nitrided 25 μm foils.…”

“…However, the production of such foils is costly, and bulk magnet synthesis is not feasible. Current research on the subject focuses on the successful production of working Fe 16 N 2 [ 18,20–27 ] permanent magnets. The main drawback to the production of bulk Fe 16 N 2 permanent magnets is that the α″‐Fe 16 N 2 body centered tetragonal (BCT) phase ( Figure ) responsible for the GSM is unstable above 212 °C; [ 7 ] therefore, the usual permanent magnet production routes, involving treatment at high temperature, [ 1 ] cannot be used.…”

Synthesis ofα′′−Fe16N2Compound Anisotropic Magnet by

“…However, none of the above bulk synthesis methods showed the possibility of producing permanent magnets because of the relatively low coercivity values obtained. Current synthesis methods for Fe 16 N 2 magnets adopts iron powder or thin foil as a precursor, which can be nitridized easily, followed by sintering or shocking to form a bulk shape [17][18][19][20][21] . For example, Ogi et al used a gas-phase method to synthesize Al 2 O 3 coated α˝-Fe 16 N 2 spherical nanoparticles with Ms to be 162 emu/g and coercivity up to 3070 Oe 17 .…”

“…For example, Ogi et al used a gas-phase method to synthesize Al 2 O 3 coated α˝-Fe 16 N 2 spherical nanoparticles with Ms to be 162 emu/g and coercivity up to 3070 Oe 17 . We have previously used a ball milling method to prepare α˝-Fe 16 N 2 particles and then compacted them into a disc magnet with the shock-compaction method 18 . Very recently, a free standing FeN foil (500 nm in thickness) with energy product up to 20 MGOe has been reported by our group recently, in which ion implantation is used for nitrogen atom introduction 19 .…”

Heavy‐Metal‐Free, Low‐Damping, and Non‐Interface Perpendicular Fe16N2 Thin Film and Magnetoresistance Device

“…The magnitude of crystalline anisotropy increases as the N doping approaches the interstitial solubility limit (N:Fe atomic ratio of 1:8) . Furthermore, upon post‐annealing of the FeN martensite at its interstitial solubility limit (Fe 8 N), a stronger magnetic crystalline anisotropy (≈10 6 J m −3 , 10 7 erg cm −3 ) can be developed because of the formation of a chemically ordered, body‐center tetragonal Fe 16 N 2 phase, as shown in Figure S2(a), Supporting Information. A strong out‐of‐plane magnetization component is observed in even partially ordered Fe 16 N 2 thin films .…”