Synthesis of Fe-Based New Magnets

Demand for high-performance magnet materials is increasing in various fields, including the automotive, electronics, and medical industries. However, the current mainstream permanent magnet materials contain rare earths and are faced with the problems of resource depletion and price escalation. Therefore, there is a need for new permanent magnet materials that do not contain rare earths. Particularly, materials with the CuAu crystal lattice structure (L1₀) have large uniaxial magnetic anisotropy, thus many studies on L1₀ type materials have been reported. However, it is a crucial problem that typical L1₀ type materials such as FePt, CoPt, and FePd include noble metals of Pt or Pd. To solve this problem, the development of novel magnetically anisotropic materials without noble metals is now eagerly expected. In this study, we aim to synthesize an L1₀ type FeNi alloy with a large magnetic anisotropy[1-4], which exists only in an iron meteorite as a Widmannstätten structure in nature. Single-phase L1₀ type FeNi powders were fabricated through a new chemical method, nitrogen insertion and topotactic extraction (NITE) [5]. In the method, FeNiN, which has the same ordered arrangement as L1₀ type 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 a chemical 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, and an actual motor was fabricated. 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. We hope that, 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.