L10 FeNi Research Articles

Computational Investigation on the Structural, Electronic and Magnetic Properties of Si-Doped L10 FeNi Alloy for Clean Energy

For the first time, this study conducts a computational analysis by employing density functional theory (DFT) to investigate the effects of silicon doping as substitutional defects on the structural, electronic, and magnetic characteristics of the L10-FeNi alloy. The aim of this study was to explore the potential applications of Si-doped FeNi compounds as alternatives to rare-earth permanent magnets. For this, we have performed full potential calculations of L10-FeNi with substitutional Si-doping within a generalized gradient approximation. Two types of substitutional Si-doping (ONi/OFe) in the Ni/Fe site of the parent alloy have been investigated. The computed formation energy (Ef) indicates that the incorporation of silicon defects increases the structural stability of tetragonally distorted L10-FeNi. Moreover, our findings demonstrate that the FeNi:Si(ONi) in the L10-structure has a stable saturation magnetization (Ms), whereas the FeNi:Si (OFe) has a small reduction in Ms. Therefore, Si-substituted FeNi alloys can be tuned to become a good candidate for permanents magnets.

Magnetic anisotropy of L1[formula omitted] FeNi (001), (010), and (111) ultrathin films: A first-principles study

In previous experiments, L10 FeNi thin films with different surfaces, including (001), (110), and (111), were produced and studied. Each surface defines a different alignment of the crystallographic tetragonal axis with respect to the film’s plane, resulting in different magnetic anisotropies. In this study, we use density functional theory calculations to examine three series of L10 FeNi films with surfaces (001), (010), and (111), and with thicknesses ranging from 0.5 to 3 nm (from 4 to 16 atomic monolayers). Our results show that films (001) have perpendicular magnetic anisotropy, while (010) favor in-plane magnetization, with a clear preference for the tetragonal axis [001]. We proposed calling this type of in-plane anisotropy fixed in-plane. A film with a surface (111) and a thickness of four atomic monolayers has a magnetization easy axis almost perpendicular to the plane of the film. As the thickness of the (111) film increases, the direction of magnetization rotates towards a tetragonal axis [001], positioned at an angle of about 45° to the plane of the film. Furthermore, the most significant changes in spin and orbital magnetic moments occur at a depth of about three near-surface atomic monolayers. Ultrathin L10 FeNi films with varying magnetic anisotropies may find applications in spintronic devices.

Efficient calculation of magnetocrystalline anisotropy energy using symmetry-adapted Wannier functions

Magnetocrystalline anisotropy, a crucial factor in magnetic properties and applications like magnetoresistive random-access memory, often requires extensive k-point mesh in first-principles calculations. In this study, we develop a Wannier orbital tight-binding model incorporating crystal and spin symmetries and utilize time-reversal symmetry to divide magnetization components. This model enables efficient computation of magnetocrystalline anisotropy. Applying this method to L10 FePt and FeNi, we calculate the dependence of the anisotropic energy on k-point mesh size, chemical potential, spin-orbit interaction, and magnetization direction. The results validate the practicality of the models to the energy order of 100[μeV/f.u.] for these systems.

Revisiting Néel 60 years on: The magnetic anisotropy of L10 FeNi (tetrataenite)

The magnetocrystalline anisotropy energy of atomically ordered L10 FeNi (the meteoritic mineral tetrataenite) is studied within a first-principles electronic structure framework. Two compositions are examined: equiatomic Fe0.5Ni0.5 and an Fe-rich composition, Fe0.56Ni0.44. It is confirmed that, for the single crystals modeled in this work, the leading-order anisotropy coefficient K1 dominates the higher-order coefficients K2 and K3. To enable comparison with experiment, the effects of both imperfect atomic long-range order and finite temperature are included. While our computational results initially appear to undershoot the measured experimental values for this system, careful scrutiny of the original analysis due to Néel et al. [J. Appl. Phys. 35, 873 (1964)] suggests that our computed value of K1 is, in fact, consistent with experimental values, and that the noted discrepancy has its origins in the nanoscale polycrystalline, multivariant nature of experimental samples, that yields much larger values of K2 and K3 than expected a priori. These results provide fresh insight into the existing discrepancies in the literature regarding the value of tetrataenite’s uniaxial magnetocrystalline anisotropy in both natural and synthetic samples.

Formation of L10 Ordering in FeNi by Mechanical Alloying and Field-Assisted Heat Treatment: Synchrotron XRD Studies.

L10-ordered FeNi, tetrataenite, found naturally in meteorites is a predilection for next-generation rare-earth free permanent magnetic materials. However, the synthesis of this phase remains unattainable in an industrially relevant time frame due to the sluggish diffusion of Fe and Ni near the order-disorder temperature (593 K) of L10 FeNi. The present work describes the synthesis of ordered L10 FeNi from elemental Fe and Ni powders by mechanical alloying up to 12 h and subsequent heat treatment at 623 K for 1000 h without a magnetic field and for 4 h in the presence of 1.5 T magnetic field. Also, to address the ambiguity of L10 phase identification caused by the low difference in the X-ray scattering factor of Fe and Ni, synchrotron-based X-ray diffraction is employed, which reveals that 6 h milling is sufficient to induce L10 FeNi formation. Further milling for 12 h is done to achieve a chemically homogeneous powder. The phase fraction of L10-ordered FeNi is quantified to ∼9 wt % for 12 h milled FeNi, which increases to ∼15 wt % after heat treatment. Heat treatment of the milled powder in a magnetic field increases the long-range order parameter (S) from 0.18 to 0.30. Further, the study of magnetic properties reveals a decrease in magnetic saturation and a slight increase in coercivity with the increase in milling duration. At the same time, heat treatment in the magnetic field shows a considerable increase in coercivity.

Effect of Pd alloying on structural, electronic and magnetic properties of L10 Fe–Ni

We present a systematic study of the effect of Pd-alloying on phase stability, electronic structure, and elastic properties in L10 Fe–Ni using density-functional theory. Being from the same group of the periodic table, Pd is the best candidate for chemical alloying. The Fe–Ni/Fe–Pd/Ni–Pd bond-length increases with increasing Pd-concentration, which weakens the hybridization between low lying energy states below Fermi-level. The reduced hybridization decreases the relative thermodynamic stability of L10 Fe(Ni1−x Pd x ) until x = 0.75. Beyond this concentration, the relative stability gets enhanced, which is attributed to a unique change in the lattice distortion (c/a). The elastic properties show a non-monotonous behavior as a function of x, which is again due to a specific change-over in the uniaxial strain. We found that Pd alloying increases the local Fe moment and structural anisotropy of L10 FeNi, which are important for applications such as microwave absorption, refrigeration systems, recording devices, imaging and sensors. We believe that the present study for the chemical alloying effect can provide critical insights toward the understanding of electronic-structure and elastic behavior of other technologically important materials.

Electronic correlation effects and local magnetic moments in L10 phase of FeNi

We study the electronic and magnetic properties of L10 phase of FeNi, a perspective rare-earth-free permanent magnet, by using a combination of density functional and dynamical mean-field theory. Although L10 FeNi has a slightly tetragonally distorted fcc lattice, we find that magnetic properties of its constituent Fe atoms resemble those in pure bcc Fe. In particular, our results indicate the presence of well-localized magnetic moments on Fe sites, which are formed due to Hund’s exchange. At the same time, magnetism of Ni sites is much more itinerant. Similarly to pure bcc Fe, the self-energy of Fe 3d states is found to show the non-Fermi-liquid behavior. This can be explained by peculiarities of density of Fe 3d states, which has pronounced peaks near the Fermi level. Our study of local spin correlation function and momentum dependence of particle-hole bubble suggests that the magnetic exchange in this substance is expected to be of RKKY-type, with iron states providing local-moment contribution, and the states corresponding to nickel sites (including virtual hopping to iron sites) providing itinerant contribution.

Structural transformations and magnetic properties of plastically deformed FeNi-based alloys synthesized from meteoritic matter

In this work we investigated FeNi-based alloys synthesized from the cosmic matter of Morasko Meteorite (MM). The fall of Morasko iron meteorite is one of the biggest known in Central Europe and it has been dated to take place about five thousand years ago. It is known that iron meteorites contain hard magnetic tetrataenite phase (L10 FeNi), which has not been synthesized on the Earth in significant amount in the bulk form yet, because of very sluggish diffusion of Fe and Ni atoms below the disorder-order temperature of 320 °C. Firstly we doped the metallic part of Morasko Meteorite with Ni to obtain nearly equiatomic composition Fe51Ni49, which is the composition of pure tetrataenite.Further synthesis steps (melt-spinning, high pressure torsion, isothermal annealing at Ta = 320 °C for τa = 720 h) were undertaken to induce structural disorder and to observe changes in the structure/microstructure of the meteorite melt with nickel and its magnetic behavior. The presence of fcc FeNi with slightly varying lattice constant was confirmed at each step of the treatment. It evolved from the initial value of a = 3.589 ± 0.001 Å in the as-quenched state, through 3.591 ± 0.001 Å after 10 revolutions in the high pressure torsion process, to the maximum value of 3.593 ± 0.001 Å after 30 revolutions of anvils. No significant impact of further application of stress (50 revolutions) was noted, as the lattice parameter changed within the uncertainty limit. After annealing, the lattice parameter decreased to the initial value of the as-quenched sample (a = 3.589 ± 0.001 Å). The observed broadening of the peaks in the X-ray diffraction patterns may be attributed to the presence of microstrains and refinement of crystallites. Both contributions were determined using the Williamson-Hall method. In the initial state, the domain sizes were of about 100 ± 17 nm and diminished to 36 ± 11 nm after application of stress. Further isothermal annealing did not change the crystallites size, which was evaluated to be 35 ± 9 nm. Microstrains in the initial state were determined as (0.039 ± 0.017)10−3 and increased significantly to (0.562 ± 0.060)10−3 after 30 revolutions of anvils. Isothermal annealing decreased microstrains to (0.215 ± 0.071)10−3. After application of stress, the coercivity and remanence were enhanced, while subsequent isothermal annealing caused their decrease. Moreover, severe plastic deformation facilitated saturation of magnetization. As-quenched sample reached saturation at a magnetic field of about 2 T, while for high pressure torsion processed alloy this value was significantly reduced.

Electronic Properties of Tetrataenite L10 FeNi at Earth’s Core Conditions

Electronic Properties of Tetrataenite L10 FeNi at Earth’s Core Conditions

Computational Design of Rare-Earth Reduced Permanent Magnets

Abstract Multiscale simulation is a key research tool in the quest for new permanent magnets. Starting with first principles methods, a sequence of simulation methods can be applied to calculate the maximum possible coercive field and expected energy density product of a magnet made from a novel magnetic material composition. Iron (Fe)-rich magnetic phases suitable for permanent magnets can be found by means of adaptive genetic algorithms. The intrinsic properties computed by ab initio simulations are used as input for micromagnetic simulations of the hysteresis properties of permanent magnets with a realistic structure. Using machine learning techniques, the magnet’s structure can be optimized so that the upper limits for coercivity and energy density product for a given phase can be estimated. Structure property relations of synthetic permanent magnets were computed for several candidate hard magnetic phases. The following pairs (coercive field (T), energy density product (kJ·m−3)) were obtained for iron-tin-antimony (Fe3Sn0.75Sb0.25): (0.49, 290), L10-ordered iron-nickel (L10 FeNi): (1, 400), cobalt-iron-tantalum (CoFe6Ta): (0.87, 425), and manganese-aluminum (MnAl): (0.53, 80).

Confirmation of Hard Magnetic L10 FeNi Phase Precipitated in FeNiSiBPCu Alloy by Anomalous X-Ray Diffraction

There is a growing interest in the development of rare-earth element-free hard magnets. The L10 FeNi phase found in Fe-based meteorites is promising based on its high-magnetocrystalline anisotropy and saturation magnetization. Not only the production, but also the characterization of L10 FeNi phase is challenging due to similar X-ray scattering factors of Fe and Ni. Here, we report on the confirmation of L10 FeNi phase precipitated in a multi-phase FeNiSiBPCu alloy by anomalous X-ray diffraction (AXRD). This is a powerful technique, which can differentiate between ordered and disordered phases along with the elements present in a phase. We measured integrated X-ray intensity with energy near the Fe (~7–7.2 keV) and Ni (8.25–8.4 keV) absorption edges for superlattice and fundamental reflections of L10 FeNi. A drastic change in integrated intensity with energy of X-ray was observed. Increase in intensity around superlattice reflection at Ni-absorption edge clearly confirms the presence of a chemically ordered L10 FeNi phase, but the results obtained at Fe edge are surprising. The analysis of AXRD results suggested that (110) diffraction peak of Fe2B phase overlaps with (001) of L10 FeNi. Understanding gained from AXRD results also allows us to estimate the long-range order parameter (S) from X-ray diffraction measurements.

L10-FeNi films on Au-Cu-Ni buffer-layer: a high-throughput combinatorial study

The fct L10-FeNi alloy is a promising candidate for the development of high performance critical-elements-free magnetic materials. Among the different materials, the Au-Cu-Ni alloy has resulted very promising; however, a detailed investigation of the effect of the buffer-layer composition on the formation of the hard FeNi phase is still missing. To accelerate the search of the best Au-Cu-Ni composition, a combinatorial approach based on High-Throughput (HT) experimental methods has been exploited in this paper. HT magnetic characterization methods revealed the presence of a hard magnetic phase with an out-of-plane easy-axis, whose coercivity increases from 0.49 kOe up to 1.30 kOe as the Au content of the Cu-Au-Ni buffer-layer decreases. Similarly, the out-of-plane magneto-crystalline anisotropy energy density increases from 0.12 to 0.35 MJ/m3. This anisotropy is attributed to the partial formation of the L10 FeNi phase induced by the buffer-layer. In the range of compositions we investigated, the buffer-layer structure does not change significantly and the modulation of the magnetic properties with the Au content in the combinatorial layer is mainly related to the different nature and extent of interlayer diffusion processes, which have a great impact on the formation and order degree of the L10 FeNi phase.

Ab initio study of magnetocrystalline anisotropy, magnetostriction, and Fermi surface of L10 FeNi (tetrataenite)

We present results of ab initio calculations of several L10 FeNi characteristics, such as the summary of the magnetocrystalline anisotropy energies (MAEs), the full potential calculations of the anisotropy constant K3, and the combined analysis of the Fermi surface and 3D -resolved MAE. Other calculated parameters are the spin and orbital magnetic moments, the magnetostrictive coefficient , the bulk modulus B0, and the lattice parameters. The MAEs summary shows rather big discrepancies among the experimental MAEs from the literature and also among the calculated MAE’s. The MAEs calculated in this work with the full potential and generalized gradient approximation (GGA) are equal to 0.47 MJ from WIEN2k, 0.34 MJ from FPLO, and 0.23 MJ from FP-SPR-KKR code. These results suggest that the MAE in GGA is below 0.5 MJ . It is expected that due to the limitations of the GGA, this value is underestimated. The L10 FeNi has further potential to improve its MAE by modifications, like e.g. tetragonal strain or alloying. The presented 3D -resolved map of the MAE combined with the Fermi surface gives a complete picture of the MAE contributions in the Brillouin zone. The obtained, from the full potential FP-SPR-KKR method, magnetocrystalline anisotropy constants K2 and K3 are several orders of magnitude smaller than the MAE/K1 and equal to kJ and 110 J , respectively. The calculated spin and orbital magnetic moments of the L10 FeNi are equal to 2.72 and 0.054 for Fe and 0.53 and 0.039 for Ni atoms, respectively. The calculations of geometry optimization lead to a c/a ratio equal to 1.0036, B0 equal to 194 GPa, and equal to 9.4 × 10−6.

Magnetic Properties of L10 FeNi Phase Developed Through Annealing of an Amorphous Alloy

Chemically ordered L10 FeNi phase observed in Fe-based meteorite has the potential to replace high-cost rare-earth-based permanent magnets in the future. However, artificial production of this phase is extremely difficult due to negligible atomic diffusion around order–disorder transition temperature (~320 °C). Here, we report a method for producing high-quality L10 FeNi phase and its magnetic properties. We show that a highly disordered metastable state, that is, amorphous can be utilized to produce a highly ordered state, which is not possible with the conventional processing techniques. Amorphous Fe42Ni41.3Si x B12− x P4Cu0.7 ( $x=0$ to 8 at.%) alloy ribbons were studied. Crystallization of amorphous ribbons at 400 °C results in adequate atomic diffusion at low temperatures to precipitate L10 FeNi grains. Structural characterization revealed a high degree of chemical ordering ( $S \ge 0.8$ ), but the volume fraction of precipitated L10 grains is low. The crystallized ribbons of FeSiBPCu are composed of two magnetic phases (hard magnetic L10 FeNi grains embedded in a soft magnetic matrix). Alloys with higher concentration of Si are shown to produce high coercivity ( $H_{c}\sim 700$ –750 Oe). The soft magnetic matrix strongly influences the H c . The actual switching field (≥3.7 kOe) of L10 FeNi has been found to be much higher than that of H c . In this paper, the L10 FeNi phase is shown to form at temperatures higher than the reported order–disorder temperature. Our results of temperature-dependent magnetization and thermal analyses suggest that the L10 FeNi phase can survive at temperatures ≤550 °C. The magnetization reversal mechanism was understood by angular dependence of $H_{c}$ , and it is shown to be a domain-wall pinning type. Due to structural and magnetic similarities between L10 FeNi and L10 FePt, ribbon samples with low-volume fraction of L10 FePt grains in a soft magnetic matrix were prepared with a similar technique. Magnetization behavior of L10 FeNi is shown to be similar to that of L10 FePt.

Resonant x-ray diffraction revealing chemical disorder in sputtered L10 FeNi on Si(0 0 1)

In the search for new rare earth free permanent magnetic materials, FeNi with a L10 structure is a possible candidate. We have synthesized the phase in the thin film form by sputtering onto HF-etched Si(0 0 1) substrates. Monatomic layers of Fe and Ni were alternately deposited on a Cu buffer layer, all of which grew epitaxially on the Si substrates. A good crystal structure and epitaxial relationship was confirmed by in-house x-ray diffraction (XRD). The chemical order, which to some part is the origin of an uniaxial magnetic anisotropy, was measured by resonant XRD. The 0 0 1 superlattice reflection was split in two symmetrically spaced peaks due to a composition modulation of the Fe and Ni layers. Furthermore the influence of roughness induced chemical anti-phase domains on the RXRD pattern is exemplified. A smaller than expected magnetic uniaxial anisotropy energy was obtained, which is partly due to the composition modulations, but the major reason is concluded to be the Cu buffer surface roughness.

Effect of Temperature/Pressure on Lattice Dynamics of FeNi

Tetratenite phase of L10 (CuAu) FeNi is identified as a hard ferromagnet in spite of that common FeNi alloys are classified as a soft magnet. Due to its strong magnetic anisotropy and large coercivity, tetrataenite phase of L10 FeNi is under investigation as a rare earth free advanced permanent magnet. Our computed equilibrium lattice constant and c/a ratio for tetratenite phase of L10 (CuAu) FeNi are in 10 % deviation with the other available results. The vibrational and electronic properties of L10 FeNi at finite temperatures/pressures are studied using the first-principles plane wave self-consistent method under the framework of density functional theory. Conclusions based on the phonon dispersion curves, phonon density of states and electronic band structure along with total and projected density of states at finite temperatures/pressures are outlined.

Lattice dynamical and thermodynamic properties of FeNi3, FeNi and Fe3Ni invar materials

The lattice dynamical and thermodynamic properties of Fe–Ni invar alloys with three stoichiometric compositions, FeNi3, FeNi and Fe3Ni, have been investigated from first principles density functional theory. Phonon dispersions of L12 FeNi3 and L10 FeNi predict dynamically stable phase along the high symmetry directions throughout the first Brillouin zone. Phonon dispersion of L12 Fe3Ni unveils a softening of transverse acoustic mode along X - M - Γ - R directions. In the phonon dispersion of D03 and Z1 phases of Fe3Ni, the significant softening of transverse acoustic mode is disappeared. Our results predict that Z1 Fe3Ni can be used as a phonon filter. The finite temperature/pressure thermodynamic properties; the isothermal bulk modulus, room temperature thermal equation of state, coefficient of thermal expansion, heat capacity, Debye temperature and Grüneisen parameter are also presented. In the D03 Fe3Ni, negative thermal expansion is observed for the temperature above 500K.

Discovery of process-induced tetragonality in equiatomic ferromagnetic FeNi

Synthesis of a new tetragonal phase at the equiatomic composition in the archetypal binary Fe-Ni phase diagram is reported. This new phase is proposed as a transitional phase linking cubic FeNi with the chemically ordered tetragonal L10 FeNi compound, tetrataenite, of interest as a new advanced permanent magnetic material. This new tetragonal phase was created in a selection of nominally equiatomic FeNi alloys, made either from natural Fe and Ni or from natural Fe combined with the 62Ni isotope, via application of high-strain processing methods followed by an annealing protocol. High-resolution neutron diffraction affirms that all unprocessed samples adopt the A1-type cubic structure (space group Fm3¯m) while all fully processed samples adopt the chemically disordered A6-type tetragonal structure (space group I4/mmm). Magnetic characterization documents a decrease in the initial magnetic susceptibility of deformed samples after annealing, evidencing a processing-induced increase in magnetic anisotropy that may be entirely accounted for by the measured tetragonal distortion. It is proposed that this new phase is a precursor to the formation of tetrataenite (L10 FeNi, space group P4/mmm), a meteoritic mineral of high magnetization and appreciable magnetocrystalline anisotropy that requires extraordinarily long cooling periods to form in nature. These results furnish new fundamental information as well as engineering insight for terrestrial synthesis of tetrataenite on industrial timescales, with high relevance for the creation of next-generation permanent magnets comprised entirely of easily accessible, earth-abundant elements.

Crystallization induced ordering of hard magnetic L1 phase in melt-spun FeNi-based ribbons

The microstructure of newly developed hard magnetic Fe42Ni41.3SixB12-xP4Cu0.7 (x = 2 to 8 at%) nanocrystalline alloy ribbons has been studied by transmission electron microscopy (TEM) and electron diffraction. A high-density polycrystalline grains, ∼30 nm in size, were formed in a ribbon after annealing at 673 K for 288 hours. Elemental mapping of the annealed specimen revealed the coexistence of three regions, Fe-rich, Ni-rich, and nearly equiatomic Fe-Ni, with areal fractions of 37%, 40%, and 23 %, respectively. The equiatomic L10-type ordered phase of FeNi was detected in between the Fe and Ni-rich phases. The presence of superlattice reflections in nanobeam electron diffraction patterns confirmed the formation of the hard magnetic L10 phase beyond any doubt. The L10 phase of FeNi was detected in alloys annealed in the temperature range of 673 to 813 K. The present results suggest that the order-disorder transition temperature of L10 FeNi is higher than the previously reported value (593 K). The high diffusion rates of the constituent elements induced by the crystallization of an amorphous phase at relatively low temperature (∼673K) are responsible for the development of atomic ordering in FeNi.

Growth of L10–FeNi thin films on Cu(001) single crystal substrates using oxygen and gold surfactants

We alternately deposited Ni and Fe monatomic layers on Cu(001) single crystal substrates and also performed surfactant-mediated growth. FeNi films exhibited a large uniaxial magnetic anisotropy (Ku) of over 0.1MJ/m3 by using an oxygen or a gold surfactant, although Ku was almost zero without surfactants. Reflection high-energy electron diffraction and atomic force microscopy indicated surfactant effects of oxygen and gold. Synchrotron X-ray diffraction indicated a formation of an L10-type ordered FeNi phase having a large Ku. We have considered that the surfactants enhanced layer-by-layer growth leading to the L10-ordering by changing a diffusion scenario of Fe and Ni atoms.