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Enhancement of hard magnetism and chemical order of synthetic L 1 0 -FeNi
An ordered tetragonal L 1 0 -FeNi, also known as meteoritic mineral tetrataenite – a promising rare-earth-free hard-magnetic compound – has been synthesized starting from a mechanochemically-activated disordered cubic A1-FeNi via formation of a chemically-ordered FeNiN intermediate and its subsequent denitrogenation and further purification of the product. The nature of a process control agent employed during the mechanochemical activation of A1-FeNi and ammonia flow velocity during the synthesis of the intermediate are two of the main factors controlling the nitrogenation. Denitrogenation with hydrogen at elevated pressures and at temperatures substantially below the order-disorder L 1 0 -FeNi → A1-FeNi transition preserves the chemical order established in the intermediate nitride. Further, post-synthesis refinement of the L 1 0 -FeNi product includes the removal of residual nitrides with a dilute acid to further improve hard-magnetic properties of the material. The L 1 0 -FeNi powders synthesized using this method exhibit a coercivity as high as 2.3 kOe and a maximum energy product reaching 6 MGOe – the highest values ever reported for a synthetic tetrataenite.
Accelerating Nature: Induced Atomic Order in Equiatomic FeNi
Abstract The production of locally atomically ordered FeNi (known by its meteoric mineral name, tetrataenite) is confirmed in bulk samples by simultaneous conversion X‐ray and backscattered γ‐ray 57 Fe Mössbauer spectroscopy. Up to 22 volume percent of the tetragonal tetrataenite phase is quantified in samples thermally treated under simultaneous magnetic‐ and stress‐field conditions for a period of 6 weeks, with the remainder identified as the cubic FeNi alloy. In contrast, all precursor samples consist only of the cubic FeNi alloy. Data from the processed alloys are validated using Mössbauer parameters derived from natural meteoritic tetrataenite. The meteoritic tetrataenite exhibits a substantially higher degree of atomic order than do the processed samples, consistent with their low uniaxial magnetocrystalline anisotropy energy of ≈1 kJ·m −3 . These results suggest that targeted refinements to the processing conditions of FeNi will foster greater atomic order and increased magnetocrystalline anisotropy, leading to an enhanced magnetic energy product. These outcomes also suggest that deductions concerning paleomagnetic conditions of the solar system, as derived from meteoritic data, may warrant re‐examination and re‐evaluation. Additionally, this work strengthens the argument that tetrataenite may indeed become a member of the advanced permanent magnet portfolio, helping to meet rapidly escalating green energy imperatives.
Nanostructure refinement and phase formation of flash annealed FeNi-based soft magnetic alloys
In this work, the resulting nanocomposite microstructures of FeNi nanocrystallites under different heating and cooling rates (5 °C/min vs 400-500 °C/s) is investigated. Conventional furnace annealing under low heating rates and slow cooling resulted in both BCC α-FeNi and FCC γ-FeNi nanocrystallites with an average grain size on the order of 25-27 nm whereas high heating rates achieved via flash annealing techniques have enabled a dramatically refined microstructure consisting of 5-7 nm grains with FCC γ-FeNi phase and found to be the dominant phase following primary crystallization. Grain size refinement and phase identity optimization yielded low values of coercivities-17 A/m and high permeability similar to 11 x 10 3 measured at 400 Hz/1 kA/m in flash annealed samples at 450 °C for 5 s. The magnetic behavior and the underlying mechanism of optimal soft magnetic properties are discussed in terms of the critical role of the grain size in domain wall pinning and coercivity.
L1 0 Ordering in MnAl and FeNi Influenced by Magnetic Field and Strain
Due to various materials supply chain challenges, magnets free of constrained elements are attracting increasing interest. Magnetic materials such as rare-earth free FeNi and MnAl have been receiving considerable attention due to the high magnetocrystalline anisotropy and other associated magnetic properties derived from their unique chemically ordered tetragonal crystal structure, denoted as the L1 0 structure. However, synthesis of L1 0 FeNi has had limited success due to the extremely low atomic mobilities of Fe and Ni. In this work, isostructural MnAl was first studied as proxy to understand the L1 0 ordering process. Here, evidence of L1 0 ordering in FeNi derived from TEM studies is presented, where ordering was facilitated by the application of strain and magnetic field provided during thermal treatment of a severely plastically deformed FeNi alloy.
Towards synthetic L 1 0 -FeNi: Detecting the absence of cubic symmetry in Laser-Ablated Fe-Ni nanoparticles
The L 1 0 crystal structure underlines an important class of chemically ordered alloys that exhibits uniaxial magnetocrystalline anisotropy. The near-equiatomic L 1 0 -FeNi extracted from meteorites has demonstrated intriguing magnetic properties for permanent magnet applications. However, the synthesis of this chemically ordered non-cubic structure has been a longstanding challenge. Here, in this work, we demonstrate the absence of cubic symmetry in near-equiatomic Fe-Ni nanoparticles synthesized by picosecond-pulsed laser ablation in liquids. The non-cubic phase detected in these particles can only be L 1 0 -FeNi or hexagonal close-packed (HCP) FeNi, and the absence of cubic symmetry was unequivocal. The orientation relationship between the non-cubic phase and the adjacent cubic phase was characterized by a series of transmission electron microscopy (TEM) techniques, which consistently suggests that the formation of the non-cubic phase involves a martensitic transformation process.
Nanostructure and compositional segregation of soft magnetic FeNi-based nanocomposites with multiple nanocrystalline phases
Soft magnetic metal amorphous nanocomposite alloys are produced through rapid solidification and thermal annealing yielding nanocrystals embedded within an amorphous precursor. Similar free energies in Co-rich and FeNi-based alloy systems result in multiple nanocrystalline phases being formed during devitrification. Studies of multi-phase crystallization processes have been reported for Co-rich alloys but relatively few have investigated FeNi-based systems. A detailed characterization of compositional partitioning and microstructure of an optimally annealed FeNi-based MANC (Fe 70 Ni 30 ) 80 Nb 4 Si 2 B 14 alloy is presented through complementary high-resolution transmission electron microscopy (HRTEM) and atom probe tomography (APT). HRTEM demonstrates orientation relationships between FCC and BCC nanocrystals, suggesting heterogeneous nucleation of nanocrystals in the amorphous matrix or a cooperative mechanism of nucleation between BCC and FCC nanocrystallites. APT results show evidence for (i) the segregation of Fe and Ni between nanocrystals of different phases, (ii) B partitioning to the amorphous phase, and (iii) an Nb-enriched shell surrounding nanocrystals.
Integrated ab initio modelling of atomic ordering and magnetic anisotropy for design of FeNi-based magnets
We describe an integrated modelling approach to accelerate the search for novel, single-phase, multicomponent materials with high magnetocrystalline anisotropy (MCA). For a given system we predict the nature of atomic ordering, its dependence on the magnetic state, and then proceed to describe the consequent MCA, magnetisation, and magnetic critical temperature (Curie temperature). Crucially, within our modelling framework, the same ab initio description of a material’s electronic structure determines all aspects. We demonstrate this holistic method by studying the effects of alloying additions in FeNi, examining systems with the general stoichiometries Fe 4 Ni 3 X and Fe 3 Ni 4 X, for additives including X = Pt, Pd, Al, and Co. The atomic ordering behaviour predicted on adding these elements, fundamental for determining a material’s MCA, is rich and varied. Equiatomic FeNi has been reported to require ferromagnetic order to establish the tetragonal L1 0 order suited for significant MCA. Our results show that when alloying additions are included in this material, annealing in an applied magnetic field and/or below a material’s Curie temperature may also promote tetragonal order, along with an appreciable effect on the predicted hard magnetic properties.
Surface Oxidation Behavior of FeNi-based Metal Amorphous Nanocomposite (MANC) Alloys for High-Speed Motor Applications
New interest in high performance soft magnetic materials (SMMs) have been fueled by the need to lower losses at higher operating frequencies while maintaining high flux density and tunable permeability in electrical motors, transformer, and generator applications. Conventional SMMs like electrical steels and Fe-based metal amorphous nanocomposite (MANC) alloys are dominated by eddy current losses at high frequencies. Recent breakthrough in high-performance FeNi MANC have shown promise in reducing eddy current losses as compared to electrical steels. Their intrinsic adherent native surface oxide layer provides sufficient electrical insulation to reduce interlaminate eddy current losses. However, notwithstanding advances in MANCs, there exists a gap in literature on investigations of the surface oxide layer responsible for significant reduction of interlaminate eddy current losses in magnetic cores. This work presents a detailed characterization of the surface oxide, oxidation behavior, and relationship between oxide thickness and resistivity of a new FeNi MANC alloy (Fe70Ni30)80Nb4B14Si2.
Data for "Integrated ab initio modelling of atomic order and magnetic anisotropy for rare-earth-free magnet design: effects of alloying additions in L1 0 FeNi."
We describe an integrated modelling approach to accelerate the search for novel, single-phase, multicomponent materials with high magnetocrystalline anisotropy (MCA). For a given system we predict the nature of atomic ordering, its dependence on the magnetic state, and then proceed to describe the consequent MCA, magnetisation, and magnetic critical temperature (Curie temperature). Crucially, within our modelling framework, the same ab initio description of a material’s electronic structure determines all aspects. We demonstrate this holistic method by studying the effects of alloying additions in FeNi, examining systems with the general stoichiometries Fe 4 Ni 3 X and Fe 3 Ni 4 X, for additives including X = Pt, Pd, Al, and Co. The atomic ordering behaviour predicted on adding these elements, fundamental for determining a material’s MCA, is rich and varied. Equiatomic FeNi has been reported to require ferromagnetic order to establish the tetragonal L1 0 order suited for significant MCA. Our results show that when alloying additions are included in this material, annealing in an applied magnetic field and/or below a material’s Curie temperature may also promote tetragonal order, along with an appreciable effect on the predicted hard magnetic properties.
Effect of pressure cycling and compression rate on the bcc-hcp transition in an FeNi alloy
Here, we investigate the body-centered cubic (bcc) to hexagonal close-packed (hcp) phase transition in Fe-10wt. %Ni alloy, combining pressure cycling and fast compression with time-resolved synchrotron x-ray diffraction in a dynamic diamond anvil cell. Three pressure cycles were conducted with compression rates ranging from 0.1 to nearly 10 3 GPa/s. During the first cycle with the slowest compression, the observed orientations in the bcc and hcp phases are consistent with the Burgers mechanism, followed by c-axis rotation of the hcp phase consistent with {$10$ $\bar{1}2$} twinning. During the following cycles with fast compression at 10 2 –10 3 GPa/s, the hcp phase exhibits negligible c-axis rotation with a nearly constant c/a ratio of ∼1.61 up to ∼30 GPa, indicating suppression of plastic deformation (especially, twinning) due to sample confinement from the gasket. Notably, the onset pressure of the transition decreases with additional pressure cycling and faster compression, which normally leads to over-pressurization. This suggests that defects or shear induced from the pressure cycling reduces the transition kinetics even during fast compression. These insights into the deformation and transition behavior in an FeNi alloy under multiple dynamic loading cycles can offer guidance for future design of advanced structural alloys and improve our understanding of planetary core processes.
Materials Data on FeNi(PO4)2 by Materials Project
FeNi(PO4)2 crystallizes in the trigonal R3 space group. The structure is three-dimensional. there are three inequivalent Fe3+ sites. In the first Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six PO4 tetrahedra and a faceface with one NiO6 octahedra. There are three shorter (1.94 Å) and three longer (2.07 Å) Fe–O bond lengths. In the second Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six PO4 tetrahedra and a faceface with one NiO6 octahedra. There are three shorter (1.95 Å) and three longer (2.08 Å) Fe–O bond lengths. In the third Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six PO4 tetrahedra and a faceface with one NiO6 octahedra. There are three shorter (1.94 Å) and three longer (2.09 Å) Fe–O bond lengths. There are three inequivalent Ni3+ sites. In the first Ni3+ site, Ni3+ is bonded to six O2- atoms to form distorted NiO6 octahedra that share corners with six PO4 tetrahedra, a faceface with one FeO6 octahedra, and a faceface with one NiO6 octahedra. There are three shorter (2.13 Å) and three longer (2.16 Å) Ni–O bond lengths. In the second Ni3+ site, Ni3+ is bonded to six O2- atoms to form NiO6 octahedra that share corners with six PO4 tetrahedra and a faceface with one NiO6 octahedra. There are three shorter (1.98 Å) and three longer (2.07 Å) Ni–O bond lengths. In the third Ni3+ site, Ni3+ is bonded to six O2- atoms to form distorted NiO6 octahedra that share corners with six PO4 tetrahedra and faces with two FeO6 octahedra. All Ni–O bond lengths are 2.15 Å. There are two inequivalent P5+ sites. In the first P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with three FeO6 octahedra and corners with three NiO6 octahedra. The corner-sharing octahedra tilt angles range from 27–51°. There are a spread of P–O bond distances ranging from 1.52–1.57 Å. In the second P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with three FeO6 octahedra and corners with three NiO6 octahedra. The corner-sharing octahedra tilt angles range from 28–51°. There are a spread of P–O bond distances ranging from 1.53–1.57 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 150 degrees geometry to one Fe3+ and one P5+ atom. In the second O2- site, O2- is bonded in a 3-coordinate geometry to one Fe3+, one Ni3+, and one P5+ atom. In the third O2- site, O2- is bonded in a bent 150 degrees geometry to one Ni3+ and one P5+ atom. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to one Fe3+, one Ni3+, and one P5+ atom. In the fifth O2- site, O2- is bonded in a bent 150 degrees geometry to one Fe3+ and one P5+ atom. In the sixth O2- site, O2- is bonded in a 3-coordinate geometry to two Ni3+ and one P5+ atom. In the seventh O2- site, O2- is bonded in a 3-coordinate geometry to one Fe3+, one Ni3+, and one P5+ atom. In the eighth O2- site, O2- is bonded in a bent 150 degrees geometry to one Fe3+ and one P5+ atom.
Materials Data on Th2(FeNi)5 by Materials Project
Th2(FeNi)5 crystallizes in the orthorhombic Pmmm space group. The structure is three-dimensional. there are two inequivalent Th sites. In the first Th site, Th is bonded in a 6-coordinate geometry to six Fe and twelve Ni atoms. There are four shorter (2.91 Å) and two longer (2.92 Å) Th–Fe bond lengths. There are eight shorter (3.20 Å) and four longer (3.22 Å) Th–Ni bond lengths. In the second Th site, Th is bonded in a 6-coordinate geometry to ten Fe and eight equivalent Ni atoms. There are a spread of Th–Fe bond distances ranging from 2.87–3.22 Å. All Th–Ni bond lengths are 3.20 Å. There are three inequivalent Fe sites. In the first Fe site, Fe is bonded in a 12-coordinate geometry to three Th, two equivalent Fe, and four equivalent Ni atoms. Both Fe–Fe bond lengths are 2.44 Å. All Fe–Ni bond lengths are 2.49 Å. In the second Fe site, Fe is bonded in a 12-coordinate geometry to three Th and six Ni atoms. There are four shorter (2.46 Å) and two longer (2.47 Å) Fe–Ni bond lengths. In the third Fe site, Fe is bonded to four equivalent Th, four equivalent Fe, and four equivalent Ni atoms to form distorted FeTh4Fe4Ni4 cuboctahedra that share corners with four equivalent FeTh4Fe4Ni4 cuboctahedra, corners with twelve NiTh4Fe5Ni3 cuboctahedra, edges with two equivalent FeTh4Fe4Ni4 cuboctahedra, edges with eight equivalent NiTh4Fe5Ni3 cuboctahedra, faces with two equivalent FeTh4Fe4Ni4 cuboctahedra, and faces with eight equivalent NiTh4Fe5Ni3 cuboctahedra. All Fe–Ni bond lengths are 2.51 Å. There are two inequivalent Ni sites. In the first Ni site, Ni is bonded to four equivalent Th, four equivalent Fe, and four equivalent Ni atoms to form distorted NiTh4Fe4Ni4 cuboctahedra that share corners with four equivalent FeTh4Fe4Ni4 cuboctahedra, corners with twelve NiTh4Fe5Ni3 cuboctahedra, edges with ten NiTh4Fe5Ni3 cuboctahedra, and faces with ten NiTh4Fe4Ni4 cuboctahedra. All Ni–Ni bond lengths are 2.49 Å. In the second Ni site, Ni is bonded to four Th, five Fe, and three Ni atoms to form distorted NiTh4Fe5Ni3 cuboctahedra that share corners with two equivalent FeTh4Fe4Ni4 cuboctahedra, corners with fourteen NiTh4Fe4Ni4 cuboctahedra, edges with two equivalent FeTh4Fe4Ni4 cuboctahedra, edges with eight NiTh4Fe4Ni4 cuboctahedra, faces with two equivalent FeTh4Fe4Ni4 cuboctahedra, and faces with eight NiTh4Fe4Ni4 cuboctahedra. There are one shorter (2.50 Å) and one longer (2.54 Å) Ni–Ni bond lengths.
Oxygen vacancy-rich amorphous FeNi hydroxide nanoclusters as an efficient electrocatalyst for water oxidation
Here, a one-pot strategy is presented to directly synthesize amorphous Fe x Ni y hydroxide nanoclusters (denoted as ANC-Fe x Ni y , <2 nm) with oxygen vacancies induced by ionic liquids. The ANC-Fe x Ni y catalyst presents abundant catalytic sites and high intrinsic conductivity. As such, the optimized ANC-Fe 1 Ni 2 exhibits high activity in oxygen evolution reaction (OER) with a Tafel slope of 39 mV dec –1 and an overpotential of 266 mV at 10 mA cm –2 . Notably, the optimized ANC-Fe 1 Ni 2 shows an extraordinarily large mass activity of 3028 A g FeNi –1 at the overpotential of 300 mV, which is ~24-fold of commercial RuO 2 catalyst. The superior activity of these Fe x Ni y hydroxide nanoclusters is ascribed to (i) the amorphous and distorted structure with abundant oxygen vacancies, and (ii) enhanced active site density by downsizing the ANC-Fe x Ni y clusters. This strategy provides a novel route for enhancing OER electrocatalytic performance and highly encouraging for the future application of amorphous metal hydroxides in catalysis.
Revisiting Néel 60 years on: The magnetic anisotropy of L1 0 FeNi (tetrataenite)
The magnetocrystalline anisotropy energy of atomically ordered L1 0 FeNi (the meteoritic mineral tetrataenite) is studied within a first-principles electronic structure framework. Two compositions are examined: equiatomic Fe 0.5 Ni 0.5 and an Fe-rich composition, Fe 0.56 Ni 0.44 . It is confirmed that, for the single crystals modeled in this work, the leading-order anisotropy coefficient K 1 dominates the higher-order coefficients K 2 and K 3 . 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 K 1 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 K 2 and K 3 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.
Magnetostrictive loss reduction through stress relief annealing in an FeNi-based metal amorphous nanocomposite
FeNi-based metal amorphous nanocomposite alloys are emerging soft magnetic materials with promise for high-speed motor applications. Here we demonstrate a technique to optimize magnetic properties in toroidal cores wound from strain annealed (Fe 70 Ni 30 ) 80 Nb 4 Si 2 B 14 amorphous metal ribbon (AMR). In-line strain annealing (SA) of the AMR yields a strip permeability that monotonically decreases with increasing SA tensions. After winding into toroidal cores, dramatic changes in magnetic properties are observed and determined to be of magnetostrictive origin. A procedure to re-anneal wound toroidal cores to reduce hysteresis and reverse magnetostrictive effects is developed inclusive of casting curvature effects. Here, we investigate re-annealing temperatures between 300 – 470 °C for cores produced from each SA condition. Magnetic core loss, W L , coercivity, H c , squareness ratio, K r , and permeability, µ r , are measured as a function of (stress relief) re-annealing temperature to optimally achieve W 1T,400Hz = 0.51 W/kg, H c = 2.42 A/m, K r = 0.22, and µ r = 35,300.
Ultrafast Preparation of Nonequilibrium FeNi Spinels by Magnetic Induction Heating for Unprecedented Oxygen Evolution Electrocatalysis
Carbon-supported nanocomposites are attracting particular attention as high-performance, low-cost electrocatalysts for electrochemical water splitting. These are mostly prepared by pyrolysis and hydrothermal procedures that are time-consuming (from hours to days) and typically difficult to produce a nonequilibrium phase. Herein, for the first time ever, we exploit magnetic induction heating-quenching for ultrafast production of carbon-FeNi spinel oxide nanocomposites (within seconds), which exhibit an unprecedentedly high performance towards oxygen evolution reaction (OER), with an ultralow overpotential of only +260 mV to reach the high current density of 100 mA cm -2 . Experimental and theoretical studies show that the rapid heating and quenching process (ca. 10 3 K s -1 ) impedes the Ni and Fe phase segregation and produces a Cl-rich surface, both contributing to the remarkable catalytic activity. Results from this study highlight the unique advantage of ultrafast heating/quenching in the structural engineering of functional nanocomposites to achieve high electrocatalytic performance towards important electrochemical reactions.
Materials Data on FeNi by Materials Project
NiFe is Tetraauricupride structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. Fe is bonded to four equivalent Fe and eight equivalent Ni atoms to form FeFe4Ni8 cuboctahedra that share corners with twelve equivalent FeFe4Ni8 cuboctahedra, edges with eight equivalent FeFe4Ni8 cuboctahedra, edges with sixteen equivalent NiFe8Ni4 cuboctahedra, faces with eight equivalent NiFe8Ni4 cuboctahedra, and faces with ten equivalent FeFe4Ni8 cuboctahedra. All Fe–Fe bond lengths are 2.51 Å. All Fe–Ni bond lengths are 2.52 Å. Ni is bonded to eight equivalent Fe and four equivalent Ni atoms to form NiFe8Ni4 cuboctahedra that share corners with twelve equivalent NiFe8Ni4 cuboctahedra, edges with eight equivalent NiFe8Ni4 cuboctahedra, edges with sixteen equivalent FeFe4Ni8 cuboctahedra, faces with eight equivalent FeFe4Ni8 cuboctahedra, and faces with ten equivalent NiFe8Ni4 cuboctahedra. All Ni–Ni bond lengths are 2.51 Å.