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 (L10-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.
The thickness dependence of the structural, static, and dynamic magnetic properties of FeCoB and Permalloy (Py) thin films deposited by RF magnetron sputtering at normal and oblique incidence was investigated. Structural analyses reveal distinct growth morphologies under oblique deposition, with FeCoB forming separated tilted columns and Py developing a bundled columnar structure through tailored deposition conditions. These microstructural differences result in markedly different magnetic behaviors. While the anisotropy field decreases slightly with thickness at normal incidence for both materials, it increases monotonically in FeCoB under oblique deposition owing to the progressive development of shape anisotropy, whereas Py exhibits a much weaker thickness dependence. The coercivity evolution reflects the competition between interfacial anisotropy, pinning, and growth-induced anisotropy. Dynamic measurements further show that the resonance frequency follows the evolution of the anisotropy field, increasing with thickness in FeCoB but decreasing in Py. FeCoB exhibits relatively homogeneous precessional dynamics and moderate permeability, whereas Py shows substantially higher low-frequency permeability together with larger relative magnetic losses. These results demonstrate that thickness-dependent columnar morphology offers an effective means of controlling magnetic anisotropy, magnetization reversal, and high-frequency response in soft magnetic thin films.
Magnon–phonon coupling can produce a magnetic-field dependence of the sound-wave velocity in magnetically ordered crystals, known as the Simon effect. Here, using a spin-lattice model of bcc Fe and the linear theory of magnetoelasticity, we investigate the Simon effect in the magnon–phonon resonance regime, where its magnitude can become particularly pronounced. We demonstrate that the finite wave vector plays a crucial role in determining the position and shape of the resonance features and can substantially modify the field dependence of the sound velocity in the low-field regime. We further analyze the dependence of the effect on the relative orientations of the magnetic field, wave-vector, and polarization directions. The results provide a more complete picture of magnetoelastic sound propagation near resonance and identify regimes where the field-induced change in sound velocity could be experimentally detectable.
