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.
Highlights
In recent years, there has been an increased demand for highly functional magnetic materials in a variety of fields, including the automotive industry, electrical and electronics industry, medicine, and environmental science, in which potential applications include wind power generation
Minute quantities of L10-FeNi are contained in iron meteorites[2,3], and it is comprised of common elements such as Fe and Ni, it has high uniaxial magnetic anisotropy (>1 × 106 J/m3)[4,5]
L10-FeNi is expected to be applied as a permanent magnet, and studies are being conducted to evaluate its fundamental properties and to develop artificial synthesis methods[4,5,7,8,9,10,11,12]
Summary
FeNi nanoparticles with an average diameter of 44 nm, fabricated using the thermal plasma method[19], were selected as the starting material to accelerate reactions during the NITE process. Topotactic denitriding is the key for the NITE method owing to the reasons described above, and the formation of ordered alloys with a scheme that is completely different from conventional methods is possible with the passing on of the atomic arrangement of nitrides after denitriding This constitutes the first successful visualization of the formation of L10-FeNi. The separate evaluation of elements with STEM-EDS is believed to have been enabled by the high S of L10-FeNi derived with the NITE method. The magnetic anisotropy improved with the formation of L10-FeNi, and Hc increased by a factor of approximately ten in comparison with that of pre-FeNi. L10-FeNi fabricated with the NITE method showed a high coercive force, as described above, and magnetization did not reach saturation even under an applied magnetic field of 2.4 MA/m. In the future, the NITE method will be developed further to facilitate the derivation of completely new ordered alloys that are superior in terms of characteristics such as magnetism, toughness, and catalytic performance
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