Synthesis of single-phase L10-FeNi magnet powder by nitrogen insertion and topotactic extraction

Abstract

Tetrataenite (L10-FeNi) is a promising candidate for use as a permanent magnet free of rare-earth elements because of its favorable properties. In this study, single-phase L10-FeNi powder with a high degree of order was synthesized through a new method, nitrogen insertion and topotactic extraction (NITE). In the method, FeNiN, which has the same ordered arrangement as L10-FeNi, is formed by nitriding A1-FeNi powder with ammonia gas. Subsequently, FeNiN is denitrided by topotactic reaction to derive single-phase L10-FeNi with an order parameter of 0.71. The transformation of disordered-phase FeNi into the L10 phase increased the coercive force from 14.5 kA/m to 142 kA/m. The proposed method not only significantly accelerates the development of magnets using L10-FeNi but also offers a new synthesis route to obtain ordered alloys in non-equilibrium states.

Nanomagnetic properties of the meteorite cloudy zone

“…Small island sizes promote uniformly magnetized (i.e., single-domain) states, while the L10 ordered tetragonal symmetry of tetrataenite generates high magnetic coercivity (up to 2 T). These two properties combine to make the cloudy zone a potent carrier of paleomagnetic information in meteorites as well as a potential sustainable replacement for rare-earth permanent magnet materials (3,4). As islands of tetrataenite form in the presence of the meteorite parent body's internally generated magnetic field, it has been proposed that the cloudy zone preserves a record of the field's intensity and polarity (5,6).…”

FeNi and Fe₁₆N₂ Magnets Prepared Using Leaching

“…The largest M s = 138 A m 2 kg ¹1 was obtained when annealed at 300°C. The value is almost the same as that of an L1 0 -FeNi powder prepared by denitriding of FeNiN (139 A m 2 kg ¹1 ), 15) but it is smaller by 10% than that of a bulk (154 A m 2 kg ¹1 ), 15) likely due to the residual Al. The largest H c was only 12 kA m ¹1 for the 400°C annealing.…”

“…7) Thus, because L1 0 -FeNi exists only in meteorites in nature, artificial syntheses must be conducted using devised techniques such as annealing with neutron irradiation under a magnetic field, 4,5) alternate deposition of Fe and Ni monatomic layers in thin-film form, 813) crystallization of melt-spun amorphous ribbons, 14) and denitriding of FeNiN. 15) The material ¡AA-Fe 16 N 2 is a metastable phase. Owing to the considerable efforts of many researchers, methods for obtaining highquality specimens have been established 16) for thin films using reactive sputtering 17) and for nanoparticles by hydrogen reduction of iron oxides followed by ammonia nitriding.…”

Synthesis of <i>L</i>1₂-FeNi Nanoparticles by Nitrogen Insertion and Topotactic Extraction Method

“…An ordered alloy of L10-FeNi 1)-3) with a structural transition temperature as low as 594 K 4)-6) was recently synthesized using the nitrogen insertion and topotactic extraction (NITE) method. 7) The NITE method consists of two steps; 1) nitriding particles of a disordered alloy to synthesize an ordered nitride compound; and then 2) topotactically removing the nitrogen 8)9) while maintaining the relative atomic positions of the other elements. Using this process, high purity L10-FeNi particles are obtained if the intermediate nitride is FeNiN.…”