A quantitative study of the thermal stability of tetrataenite (L10 FeNi) for sustainable permanent magnets

The ferromagnetic compound tetrataenite has attracted considerable attention as a compelling permanent magnet candidate free of critical elements for current and next-generation advanced technologies. Comprised solely of Fe and Ni, tetrataenite exhibits a large and remarkably stable magnetic flux density derived from its atomically ordered (L1 0 -type) crystal structure that imparts high magnetocrystalline anisotropy. However, macroscopic quantities of tetrataenite are only formed naturally over millions of years in ancient planetary bodies, and its synthesis on earth remains a formidable challenge. Here, the mechanisms of atomic disordering of tetrataenite and its thermal stability were investigated in natural materials obtained from a meteoritic source. Time- and temperature-dependent atomic disordering profiles, derived from the degradation of coercivity during progressive thermal treatment, were created and analyzed using a metallurgical-inspired kinetic model. The thermally driven phase transformation from ordered (tetrataenite) to disordered (taenite) FeNi is deduced to initiate from pre-existing motes of atomic disorder and to proceed under progressively higher energy barriers that slow the transformation. Results allow quantification of tetrataenite's thermal stability at elevated temperatures, a characteristic that is relevant both to formation from the atomically disordered state and to contemplated high-temperature applications. These outcomes provide realistic estimates of tetrataenite's potential performance as a permanent magnet and inform developmental pathways toward sustainable, critical-element-free permanent magnets