L10-FeNi Phase Research Articles

Promoting the ordering of L10-FeNi phase via chemical interactions with substrate: A molecular dynamics simulation study

The L10-type FeNi intermetallic phase is an important rare-earth-free magnetic material. However, its fabrication remains challenging. In this paper, we propose a chemical-interaction-enhanced ordering mechanism in vapor deposition processes, which is supported by molecular dynamics deposition simulations. Additionally, we describe guidelines for the fabrication of further ordered intermetallic thin films. Thus, we present not only the fabrication of an L10-type FeNi intermetallic magnet but also guidelines for developing diverse structural and functional layer-ordered intermetallic materials.

Effect of Co addition on hard magnetic properties of annealed Fe-Ni-P amorphous alloys dominated by L10-FeNi phase

Annealing FeNi-based amorphous alloys is a promising way to fabricate rare-earth-free L10-FeNi hard magnetic materials. In this study, the effect of Co addition on the magnetic properties of annealed Fe-Ni-P alloys has been investigated. With Co addition, the coercivity of optimized Fe38Ni38Co8P16 alloys reaches 1145 Oe, which can be attributed to the enhanced magneto-crystalline anisotropy of the L10 phase since the remnant coercivity in the out-of-plane direction increases towards 2.35 kOe. By comparing the hysteresis loss and the theoretical magneto-crystalline anisotropic energy of L10-FeNi, the mean volume fraction of L10 phase is estimated to be ∼5.5%. The study suggests that Co addition is greatly beneficial to the fabrication of L10-FeNi hard magnetic materials, and this process has a large potential to be further improved.

Micromagnetic modelling of nanorods array-based L10-FeNi/SmCo5 exchange-coupled composites

Exchange-coupled nanocomposites are considered as the most promising materials for production of high-energy performance permanent magnets, which can exceed neodymium ones in terms of energy product. In this work, micromagnetic simulations of L10-FeNi/SmCo5 composites based on the initially anisotropic structure of nanorods array were performed. Texturing effect on magnetic properties was investigated. It was revealed that even 30% of anisotropy axes misalignment of grains in L10-FeNi phase would lead to only ≈10% drop of coercivity. To maximize magnetic properties of the composites, parameters of microstructure were optimized for 120 × 120 array of interacting nanorods and were found to be 40 nm nanorod diameter and 12–20 nm interrod distance. The estimated diameter of nanorods and the packing density of the array provide energy product values of 149 kJ m−3. Influence of interrod distance on energy product values was explored. Approaches for production of exchange-coupled composites based on anisotropic nanostructures were proposed.

Properties of a rare earth free L10-FeNi hard magnet developed through annealing of FeNiPC amorphous ribbons

The rare-earth-free hard magnetic L10-FeNi phase found in cosmic meteorites demonstrates potential as a next-generation permanent magnet. However, it is very difficult to artificially produce the L10-FeNi phase due to the low atomic diffusion coefficients of Fe and Ni near the order-disorder transition temperature (∼320 °C). Therefore, FeNiPC amorphous alloy systems exhibiting crystallization temperature (Tx) near the transition temperature were investigated. The amorphous alloys were annealed at Tx, resulting in high atomic diffusion. The structural and microstructural characterizations of annealed ribbons revealed the formation of L10-FeNi phase through observation of the superlattice peak. The magnetic property, such as coercivity (Hc), also indicated the formation of L10-FeNi phase, because the maximum Hc value is 641 Oe after the annealing process.

Fabrication of L1-FeNi by pulsed-laser deposition

We demonstrated the fabrication of a rare-earth-free ferromagnetic L10-type Fe–Ni alloy (L10-FeNi) by pulsed laser deposition (PLD). We deposited Fe and Ni on Cu(001) by alternating monoatomic deposition via automatically stabilized laser ablation. We examined the structural properties, magnetic properties, and surface morphology of the alloy specimens as the growth temperature (Ts) was varied. We adequately confirmed the construction of the most prominent L10-FeNi phase at 300 °C, which is significantly higher than previously reported growth temperatures, indicating that PLD followed by thermal treatment promoted two-dimensional growth of the adsorbent. The formation process of L10-FeNi was investigated from the standpoint of surface thermodynamics, and the results suggest that the surface free energy of PLD and its highly instantaneous deposition process by PLD played key roles. Our findings are expected to lead to advanced methods for the fabrication of L10-FeNi.

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.

Fabrication of L10-FeNi phase by sputtering with rapid thermal annealing

FeNi films were directly deposited on MgO(001) substrates by co-sputtering and rapid thermal annealing (RTA). The formation of the L10 phase was investigated for films with different thicknesses and different annealing conditions by grazing incidence X-ray diffraction. For the FeNi films with a thickness of 5 nm, superlattice 001 and 110 peaks were observed after annealing at a heating rate of 50 °C/s, which indicates that three variants of L10 grains were formed in the films. The maximum long-range order parameter, which corresponded to a volume-averaged parameter, was approximately 0.11. For the FeNi films with a thickness of 30 nm, a superlattice 110 peak was only observed after annealing at a heating rate of 50 °C/s, and the formation of 001 textured grains was clarified. Magnetic properties also changed depending on the FeNi film structures. The formation mechanism of L10-FeNi is discussed based on the strain caused by RTA in the FeNi films.

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.

Thermodynamic and kinetic parameters of the chemical order–disorder transformation in L10 FeNi (tetrataenite)

The thermodynamic and kinetic parameters describing the chemical disordering process of L10 FeNi (tetrataenite) are quantified through analysis of calorimetric data obtained from material (Fe57Ni43) extracted from the NWA 6259 meteorite. The material presents an endotherm with peak temperatures of 800–860 K depending on heating rate and a transformation enthalpy of 4.0 ± 0.2 kJ/mol of atoms that corresponds to the L10 → A1 chemical order–disorder phase transformation. Using reported values of the enthalpy of mixing of the A1 phase and the enthalpy difference between the A1(γ) and the A2(α) phases of Fe, the enthalpy of formation of the L10 phase at the composition 43 at.% Ni constituted from Fe and Ni in their standard state is calculated as −4.4 ± 0.6 kJ/mol of atoms. These results indicate that the L10 FeNi phase is at the edge of enthalpic stability relative to a mixture of α-Fe and L12 FeNi3. The measured kinetic chemical-disordering transformation temperature is well above the reported order–disorder temperature of 593 K (320 °C) confirming that the disordering process is highly kinetically limited. The activation energy of chemical disordering of L10 FeNi (43 at% Ni) is 3.08 ± 0.07 eV/atom. Results obtained in this study are consistent with a model of one-dimensional growth of the disordered phase wherein the transformation rate is limited by the creation and migration of vacancies. Establishment of the enthalpy difference between the chemically-ordered and -disordered phases as well as determination of the activation energy for transformation provide guidance for laboratory synthesis of the L10 FeNi phase, which is of significant applied interest as a new advanced permanent magnet material.

Artificially produced rare-earth free cosmic magnet.

Chemically ordered hard magnetic L10-FeNi phase of higher grade than cosmic meteorites is produced artificially. Present alloy design shortens the formation time from hundreds of millions of years for natural meteorites to less than 300 hours. Electron diffraction detects four-fold 110 superlattice reflections and a high chemical order parameter (S 0.8) for the developed L10-FeNi phase. The magnetic field of more than 3.5 kOe is required for the switching of magnetization. Experimental results along with computer simulation suggest that the ordered phase is formed due to three factors related to the amorphous state: high diffusion rates of the constituent elements at lower temperatures when crystallizing, a large driving force for precipitation of the L10 phase, and the possible presence of L10 clusters. Present results can resolve mineral exhaustion issues in the development of next-generation hard magnetic materials because the alloys are free from rare-earth elements, and the technique is well suited for mass production.

Structural and magnetic properties of FeNi thin films fabricated on amorphous substrates

FeNi films were fabricated by sputtering and rapid thermal annealing on thermally amorphous substrates to realize the formation of an L10-FeNi phase by a simple method. Structural and magnetic properties of FeNi films were investigated by varying the annealing temperature. L10-FeNi superlattice peaks were not observed in X-ray diffraction patterns, indicating no formation of L10-ordered phase, however, the surface structure systematically changed with the annealing temperature. Magnetization curves also revealed a drastic change depending on the annealing temperature, which indicates the close relation between the morphology and magnetic properties of FeNi films fabricated on amorphous substrates.

Addition of Co to L10-ordered FeNi films: influences on magnetic properties and ordered structures

L10-type ordered FeNi alloy is a good candidate material for rare-earth-free permanent magnets due to its large saturation magnetization, large uniaxial magnetic anisotropy (Ku) and high Curie temperature. Previously, we investigated the fundamental properties of L10–FeNi by preparing single crystal films by alternate deposition of Fe and Ni monatomic layers. In the present study, we investigated the influences of the addition of Co on the magnetic and structural properties of L10-type ordered FeNi films. Three types of Co addition, with the substitution of Fe layers, Ni layers and both layers, were performed. X-ray diffraction using synchrotron radiation indicated that Co atoms were randomly distributed in films in all addition processes. A long-range order parameter of the L10–FeNi phase and Ku showed a tendency to decrease with the amount of Co for additions substituting Fe layers and both layers. However, Ku showed no decrease with Co addition substituting ⩽10% of Ni layers, even though the order parameter notably decreased. This indicates that an achievement of the Co addition substituting Ni atoms without any reduction of the order parameter enhances Ku in L10–FeNi.

Structural, magnetic and electronic state characterization of L1 0-type ordered FeNi alloy extracted from a natural meteorite

To understand the hard magnetism of L10-type ordered FeNi alloy, we extracted the L10-FeNi phase from a natural meteorite, and evaluated its fundamental solid-state properties: sample composition, magnetic hysteresis, crystal structure and electronic structure. We executed multidirectional analyses using scanning electron microscopy with an electron probe micro-analyzer (SEM-EPMA), a superconducting quantum interference device (SQUID), x-ray diffraction (XRD) and magnetic circular dichroism (MCD). As a result, we found that the composition was Fe: 50.47 ± 1.98 at.%, Ni: 49.60 ± 1.49 at.%, and an obvious superlattice peak is confirmed. The estimated degree of order was 0.608, with lattice constants a = b = 3.582 Å and c = 3.607 Å. The obtained coercivity was more than 500 Oe. MCD analysis using the K absorption edge suggests that the magnetic anisotropy could originate from the orbital magnetic moment of 3d electrons in Fe; this result is consistent with that in a previous report obtained with synthetic L10-FeNi.