United States

Epsilon iron oxide (ε-Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;) is a nanoscale iron oxide polymorph with a large coercive field value (&amp;gt; 20 kOe at room temperature). High yield ε-Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; syntheses involve the use of a SiO&lt;sub&gt;2&lt;/sub&gt; matrix to prevent agglomeration during high temperature sintering (&amp;gt; 900°C).&lt;sup&gt;1-3&lt;/sup&gt; Herein, we present a new synthesis method of ε-Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; at low temperature and ambient pressure which uses no protective matrix, via a precursor of Prussian blue with a small amount of embedded ε-Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; nanoparticles.&lt;br/&gt;Core ε-Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; nanoparticles, prepared using a standard method,&lt;sup&gt;4&lt;/sup&gt; were sonicated in K&lt;sub&gt;4&lt;/sub&gt;[Fe(CN)&lt;sub&gt;6&lt;/sub&gt;]&lt;sub&gt;(aq)&lt;/sub&gt; solution before 2M HCl&lt;sub&gt;(aq)&lt;/sub&gt; was added. The obtained sample (denoted core-shell) was sintered in air at 300°C, 400°C and 500°C for 2 hours.&lt;br/&gt;Fig. 1a shows TEM images of the core-shell, 300°C, 400°C and 500°C sintered samples. ε-Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; nanoparticles are shown to have spherical morphology, d&lt;sub&gt;TEM&lt;/sub&gt; = 23 ± 7 nm, whereas Prussian blue nanocrystals are larger cubic or spherical particles. The sintered samples at 300°C, 400°C and 500°C show aggregations of spherical and cubic nanoparticles which become more distinct as the temperature increases.&lt;br/&gt;Fig. 1b shows the XRD spectra with Rietveld analysis. The core-shell sample shows peaks assigned to ε-Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; (24%, orthorhombic, Pna2&lt;sub&gt;1&lt;/sub&gt;) and Prussian blue (76%, cubic, Fm3m). In the sintered samples, Prussian blue peaks are not present, though the peaks corresponding to the core ε-Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; remain with the particle size calculated via the first principles method consistent in all samples, ca. 25 nm. At 300°C, a second phase of ε-Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; and γ-Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; with particle sizes ca. 3 nm are present, alongside a small amount of α-Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;. At 400°C, the proportion of small size Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; nanoparticles decreases, and the proportion of ca. 25 nm ε-Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; and α-Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; increases. At 500°C, the only phases present are ca. 25 nm ε-Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; (92%) with a small amount of macroscale α-Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; (8%).&lt;br/&gt;Prussian blue was shown to convert to ε-Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; at high yield when sintered at 500°C in the presence of ε-Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; core nanoparticles. This is the lowest temperature ε-Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; has been reportedly prepared at in ambient pressures and may pave the way to a lower energy synthesis method for this hard magnetic ferrite.

![](https://assets.underline.io/uploads/markdown_image/1/image/0df521fdb3bc1ce80c3606233fef2f93.jpg)

Fig. 1 a) TEM images and b) XRD spectra of respective samples

2022 Joint MMM-INTERMAG

The Formation of a Nanoscale Hard Magnetic Ferrite from Prussian Blue Nanocrystals

The 15th Joint MMM-INTERMAG Conference (2022 Joint) is sponsored jointly by AIP Publishing and the IEEE Magnetics Society. Members of the international scientific and engineering communities interested in recent developments in fundamental and applied magnetism are invited to attend and contribute to the technical sessions. The technical program will include invited and contributed papers in oral and poster sessions, invited symposia, a plenary session, and an evening session, with about 1500 presentations overall. This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

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Epsilon iron oxide (ε-Fe2O3) is a nanoscale iron oxide polymorph with a large coercive field value (&gt; 20 kOe at room temperature). High yield ε-Fe2O3 syntheses involve the use of a SiO2 matrix to prevent agglomeration during high temperature sintering (&gt; 900°C).1-3 Herein, we present a new synthesis method of ε-Fe2O3 at low temperature and ambient pressure which uses no protective matrix, via a precursor of Prussian blue with a small amount of embedded ε-Fe2O3 nanoparticles. Core ε-Fe2O3 nanoparticles, prepared using a standard method,4 were sonicated in K4[Fe(CN)6](aq) solution before 2M HCl(aq) was added. The obtained sample (denoted core-shell) was sintered in air at 300°C, 400°C and 500°C for 2 hours. Fig. 1a shows TEM images of the core-shell, 300°C, 400°C and 500°C sintered samples. ε-Fe2O3 nanoparticles are shown to have spherical morphology, dTEM = 23 ± 7 nm, whereas Prussian blue nanocrystals are larger cubic or spherical particles. The sintered samples at 300°C, 400°C and 500°C show aggregations of spherical and cubic nanoparticles which become more distinct as the temperature increases. Fig. 1b shows the XRD spectra with Rietveld analysis. The core-shell sample shows peaks assigned to ε-Fe2O3 (24%, orthorhombic, Pna21) and Prussian blue (76%, cubic, Fm3m). In the sintered samples, Prussian blue peaks are not present, though the peaks corresponding to the core ε-Fe2O3 remain with the particle size calculated via the first principles method consistent in all samples, ca. 25 nm. At 300°C, a second phase of ε-Fe2O3 and γ-Fe2O3 with particle sizes ca. 3 nm are present, alongside a small amount of α-Fe2O3. At 400°C, the proportion of small size Fe2O3 nanoparticles decreases, and the proportion of ca. 25 nm ε-Fe2O3 and α-Fe2O3 increases. At 500°C, the only phases present are ca. 25 nm ε-Fe2O3 (92%) with a small amount of macroscale α-Fe2O3 (8%). Prussian blue was shown to convert to ε-Fe2O3 at high yield when sintered at 500°C in the presence of ε-Fe2O3 core nanoparticles. This is the lowest temperature ε-Fe2O3 has been reportedly prepared at in ambient pressures and may pave the way to a lower energy synthesis method for this hard magnetic ferrite.

![](https://assets.underline.io/uploads/markdown_image/1/image/0df521fdb3bc1ce80c3606233fef2f93.jpg)

Fig. 1 a) TEM images and b) XRD spectra of respective samples

technical paper

The design and discovery of new functional materials has acquired a sense of urgency recently for critical-elements reasons. In the case of permanent magnets, computational and experimental methods are being used synergistically to aid the search for new materials with large values of saturation magnetization Ms, anisotropy K, and Curie temperature Tc [1-3]. Ideally, the materials exhibit μoMs &gt; 0.8 T and K &gt; 1.5 MJ/m3. Another criterion for the evaluation of new permanent-magnet materials before the typically difficult task of synthesis and coercivity development is the hardness parameter κ = (K/μoMs2)1/2 [3]. This parameter can also be written as κ = (Ha/2Ms)1/2, where Ha = 2K/μoMs is the anisotropy field, so that each value of κ yields a straight line when Ha is plotted vs. Ms. Ideally, κ is comparable to or larger than one [3, 4]. Figure 1(a) combines the Ms and κ requirements to yield an area of promising permanent magnets (yellow). However, the main figure of merit in permanent magnets energy product. Figure 1(b) plots K against Ms, which has several advantages: (i) the blue isoenergetic curves show the expected maximum energy product, (ii) real-structure factors such a remanence ratio, Kronmüller factor α, packing fraction, and loop shape easily be included in the isoenergetic curves; and (iii) the primary intrinsic properties are K and Ms, not Ha and Ms. If the boundary of the yellow area and blue curves were physically equivalent, the boundary and the blue curves would be approximately parallel. This in not the case for the ascending branch of the boundary, where the curves are almost perpendicular due to the very different natures of hardness and energy product. Aside from helping to identify promising permanent-magnet materials, this work underlines the long-term aspect of permanent-magnet development. The work in Nebraska is supported by NSF-DMREF (No. 1729288), NSF-EQUATE (OIA-2044049), the NU Collaborative Initiative, and NCMN, whereas the research at Ames is funded by DOE.

![](https://assets.underline.io/uploads/markdown_image/1/image/115daa171706731e49904daa3478c12a.jpg)

Fig. 1. Permanent-magnet performance plots: (a) Ha-Ms plot and (b) K-Ms plot, the axes showing μoH and μoM. The specific model used for the blue curves assume Mr = Ms, a straight M(H) line in the second quarter, and α = 0.4.

Criteria for Permanent-Magnet Materials

Additive manufacturing based on selective laser melting (SLM) promises versatile new opportunities for hard magnetic materials as key materials for electrification. However, SLM technology is challenging, especially for today’s strongest permanent magnets based one rare earth (RE) metals. It requires special processing chambers to handle the powders sensitive to oxidation. SLM of RE-based permanent magnet material so far was mainly performed on nanocrystalline Fe-Nd-B powder with overstoichiometric Fe content (e.g. MQP-S from Magnequench). Recently, it has been shown, that due to rapid solidification in SLM, a nanocrystalline microstructure with hard magnetic properties develops in the bulk [1]. In addition, the development of very fine Fe-Nd-B microstructures with directed crystal growth and finely dispersed Nd-rich phase is possible [2]. Material systems such as Co-Sm or Fe-Pr-Cu-B can offer advantages for SLM processing. Due to their solidification process and phase equilibria, they form magnetically advantageous microstructures. Permanent magnet properties can be obtained by annealing, without the need of subsequent powder metallurgical processing or rapid quenching. By a proper choice of processing parameters and post-annealing conditions good permanent magnet properties and partial magnetic anisotropy can be realized for printed parts of both materials. In the case of (CoCuFeZr)17Sm2 a coercivity of 2.77 T, remanence of 0.78 T and maximum energy density of 109 kJ/m3 have been achieved (Fig. 1). Due to texture of the printed parts the remanence is 24 % higher than for a comparable isotropic sintered magnet. In the case of FePrCuB a coercivity of 0.67 T, remanence of 0.67 T and maximum energy density of 69.8 kJ/m3 have been obtained (Fig. 2). Due to higher degree of texturing, the printed parts so far exhibit a 26 % higher remanence compared to identically annealed cast material of the same composition. The paper highlights the correlation between microstructure and related magnetic properties for the processing parameter-sets used.

![](https://assets.underline.io/uploads/markdown_image/1/image/d5437add5e448b415f456c06c19ea099.jpg)

Fig. 1: Microstructural and magnetic properties of (CoCuFeZr)17Sm2 SLM-printed component.

![](https://assets.underline.io/uploads/markdown_image/1/image/a4d614fb9e936909233821d79c9817cc.jpg)

Fig. 2: Microstructural and magnetic properties of FePrCuB SLM-printed component.

Selective Laser Melting of Partially Anisotropic Rare Earth-based Permanent Magnets

Abstract: Compared with the widely used industrial production process of sintering, hot deformation (HD) process has many advantages and it was once considered as a candidate technology for the fourth generation rare earth permanent magnets. At present, the research of HD Nd-Fe-B magnets mainly focuses on the magnet preparation and microstructure control[1]. One-step HD can shorten the preparation process of bulk anisotropic magnets to the minimum, which highlights the advantages of simple high-definition process. However, there are still many aspects of this method that have not been systematically studied in depth. In this study, the effects of deformation ratio and temperature on the microstructure and properties of NdFeB magnets were studied by adjusting the one-step HD process. The results show that the optimized magnetic properties with Hcj, Jr and (BH)max of 960 kA/m, 1.2 T and 33 MGOe are obtained at 750 oC with 80% deformation ratio, which are very close to the performance of ordinary hot pressing/hot deformation (HP/HD) magnets, as shown in Fig. 1 (a). The microstructure and corrosion resistance were studied. The results show that with the increase of HD temperature and deformation rate, the corrosion resistance of the magnet first increases and then decreases, and the platelet grains become more obvious. When the HD temperature exceeds 750 oC and the deformation exceeds 80%, the grain growth is too large and the grain boundary thickness decreases sharply. After 90%, there is no grain boundary phase and the grain shape of the two deformed magnets is basically the same, as shown in Fig. 1 (b). It can be considered that one-step HD can replace HP/HD and achieve the simplest process while maintaining the performance [2]. As shown in Figs. 1 (c) (d), with the increase of deformation rate and HD temperature, the magnetic energy product and remanence first increase and then decrease, and the coercivity monotonously decreases.

![](https://assets.underline.io/uploads/markdown_image/1/image/619f224750bb04aa175f6fb5c5df58c9.jpg)

Effects of deformation ratio and temperature on microstructure and properties of NdFeB magnets by one-step hot deformation

Abstract Grain boundary diffusion (GBD) provides a promising way for Nd-Fe-B magnets to obtain high coercivity with less consumption of critical rare earths (RE). With the expansion of application field, the mechanical and anti-corrosion properties of Nd-Fe-B magnets has attracted increasing attention except their magnetic properties. Here, we proposed a strategy to simultaneously enhance these properties by GBD without employing heavy rare earths (HRE). The diffusion sources of Pr70Al20Cu10 (PrAlCu) and Al75Cu25 (AlCu) were prepared by arc melting. The thickness of initial magnet is 4.5 mm. The results show that the coercivity can be enhanced from 1000 to 1346 and 1089 kA/m by diffusion of PrAlCu and AlCu, respectively (Fig. 1(a)). Interestingly, the compression strength of the magnets also increased by 485 and 252 MPa, respectively. In addition, it is found that AlCu diffusion can improve the corrosion resistance of the magnets, which is different from that of PrAlCu [1]. The microstructure analysis showed that PrAlCu diffusion leads to the formation of continuous grain boundary (GB) layers for magnetic decoupling and strong binding between 2:14:1 grains (Fig. 1(b)). Although the non-RE diffusion source of AlCu shows less efficiency in increasing the content of RE-rich GB phases (Fig. 1(c)), it reduces the defects at interfaces, which is helpful for hindering the reversal domain nucleation [2, 3], as shown in Figs. 1(d1) to (d3). The modified GBs by AlCu diffusion also are effective for crack bridging or buffering, and exhibit an enhanced chemical stability. The high-abundance elements La/Ce based diffusion sources are also investigated in this work. The present results indicate that GBD of the HRE-free low-melting alloys can be used to effectively improve both the magnetic and service performance of Nd-Fe-B magnets due to the optimized microstructure.

![](https://assets.underline.io/uploads/markdown_image/1/image/1d95088594a90e4bd612c377f5970c41.jpg)

A strategy to enhance magnetic and service performance of Nd-Fe-B magnets by HRE-free grain boundary diffusion

The theory on exchange spring magnets, published by Kneller and Hawig in 1991, heralded the next big leap forward in the field of advanced permanent magnets. The theory predicted that a magnet prepared by combination of a hard and a soft magnetic phase would exhibit an improved remanent magnetization, Mr, as long as the two phases were mutually exchange coupled [1]. However, accomplishing an actual improvement has proven rather challenging. When large particles of soft phase are strongly exchange coupled to a hard phase, a magnetic softening is induced, instead of the desired hardening [2]. However, moderate Mr enhancements have been detected in exchange-decoupled composites [3]. The dominant magnetic interactions in exchange decoupled systems are magnetodipolar [4]. Therefore, exploiting the dipolar interactions between exchange decoupled hard and soft phases is an alternative strategy to prepare magnetic composites with an enhanced performance [5]. The efficacy of the method relies on controlling the magnitude of the self demagnetizing fields, which strongly depends on the size and shape of the soft phase. Here, exchange decoupled SrFe12O19 (hard)/Fe (soft) composites have been prepared, both in powder and injection moulded magnet dense form. The influence of the size of the soft phase has been experimentally studied, covering a range between 25 nm and 11 µm. Micromagnetic simulations have been carried out for the specific system in order to understand the spin dynamics inside the soft grains (see Figure 1). Regardless of the soft phase dimensions, the composites show a larger Mr than predicted by the theory. In fact, we observe and report here for the first time an increase in remanence in hard-soft injection moulded magnets in the absence of exchange coupling. Micromagnetic simulations point at the existence of a vortex like state at the core of the Fe particles, which orients with the internal field created by the ferrite particles, as the reason for this increase in remanence. Figure 1. (a) experiment; (b) micromagnetic simulations at remanence and (c) at coercivity. The authors would like to thank financial support from the European Commission through the project AMPHIBIAN (H2020 NMBP 2016 720853).

![](https://assets.underline.io/uploads/markdown_image/1/image/feaa7141cd372b61bcc43aab2e22a4ad.jpg)

Remanence Improvement in Exchange-Decoupled Composites Owing to Dipolar Interactions

Exchange spring hard-soft magnetic nanocomposites (NCs) are proposed as potential high-performance magnets [1,2]. Their relatively poor performance [3-6] compared to predicted values [7] is attributed to insufficient control over the size and distribution of the soft phase. In this work e-beam lithography was used to control the size, shape and position of soft magnetic (FeCo) nano-rods embedded in a micro-patterned hard magnetic matrix (25 nm thick FePt-L10). We report a study of samples with different nanorod widths (24 and 120 nm) and comparable volume content. Their global M(H) loops have similar Hc values, but that of the sample with wide nanorods is concave (Fig. 2a), and First Order Reversal Curve diagrams reveal that this sample has some uncoupled soft magnetic phase. Uncoupled soft phase reversal is confirmed by MFM imaging in different remanent states, where hard and soft phase switching can be distinguished owing to the different length scales of the patterns (Fig. 1). Micromagnetic modelling (MuMax3) was performed to simulate magnetization reversal and MFM contrast. Good agreement is obtained between the measured (Fig. 2a) and simulated (Fig. 2b) data. Magnetization distribution cross-sections during reversal indicate that the wide soft rods reverse independently of the hard matrix, while the narrower rods are coupled during the entire reversal process (Fig. 2c-e). Convoluting results of stray field distributions at the experimental scan height with an MFM probe modelled as a monopole, we obtained comparable images with periodic patterns with the same length scale as the nanorods (Fig. 2f-g). The use of MFM remanent imaging combined with simulations to study magnetization reversal will be discussed in the framework of a broader study of model soft in hard nanocomposites.

![](https://assets.underline.io/uploads/markdown_image/1/image/97f767231afaf37c18391fe56fc92af6.jpg)

MFM images of NCs in remanent state, after applied field of 250 mT (left) and 500 mT (right), for rod widths of 24 nm (a,c) and 120 nm (b,d). Inserts - SEM plan view images of the nanorods (1 µm scale bar).

![](https://assets.underline.io/uploads/markdown_image/1/image/0304cf4965480752d8cca3cfd62a8896.jpg)

a) Experimental M(H) loops; b) Simulated demagnetization curves. c-e). Magnetization maps at the height of the rod (numbers indicate position along the demag curve). Simulated (f) and experimental (g) MFM contrast.

Magnetization reversal in nanofabricated soft-in-hard exchange-spring magnets

Where the high-performance permanent magnets are needed (e.g. in the area of ‘green’ energy technology, such as electric vehicles and windmills) rare-earth (RE) magnetic materials dominate. At the same time, the heavier RE elements are quite expensive, some of them are rapidly decreasing in availability, and are often mined with the methods that leave an environmental footprint. Additionally, nowadays, there is a gap between the ‘strong’ RE-based magnets and their RE-free alternatives. We are using the data-mining approach in the search for high (and medium)-performance RE-free/lean magnetic materials. Filtering through a large number of known structures from ICSD database [1], we are looking for materials with high magnetization M &gt; 1 T, uniaxial MAE &gt; 1 MJ/m3, and Tc &gt;300 K. Sometimes, additional elements alterations are attempted to tweak the properties that are below the required values or make the material more cost-effective. Two searches have already been performed – a search amongst the materials containing a 3d- and a 5d-elements [3] and the materials that contain at least two 3d- metals [4]. New material was found (that had not been used as a permanent magnet before) and consequently synthesized by our experimental collaborators – Co3Mn2Ge [4]. From the ab-initio calculations, the defect-free material was predicted to have the saturation magnetization of 1.71 T, the uniaxial magnetocrystalline anisotropy of 1.44 MJ/m3, and the Curie temperature of 700 K. The samples synthesized, however, were found to have a partial disorder of Co and Ge. A saturation polarization of 0.86 T at 10 K was detected, together with a uniaxial magnetocrystalline anisotropy constant of 1.18 MJ/m3, and the TC = 359 K. These magnetic properties make Co3Mn2Ge a very promising material to be considered as a rare-earth free permanent magnet. Its magnetism depends critically on the amount of disorder of the Co and Ge atoms, a further improvement of the magnetism is possible. The next high-throughput search is being currently performed in collaboration with the experimental colleagues. We would like to acknowledge the financial support of the SSF and SNIC for the computation resources.

High-throughput and Data-mining Search for Novel Rare-Earth-Free Permanent Magnets

Permanent magnets (PMs) are indispensable in sectors as important as energy and electromobility. MnAlC is an excellent rare earth-free candidate to contribute to fill the gap existing between ferrites and NdFeB magnets, provided a successful development of its PM properties. This will be only possible by combining a high magnetization, through a maximized content of the only ferromagnetic phase in the MnAl system (τ-phase), and an enhanced coercivity, through efficient nanostructuring and phase transformation [1]. We have recently shown the importance of combining the formation of the β-Mn phase and Mn3AlC to increase coercivity -while maintaining a high remanence- in both powder and bulk MnAlC magnets produced by a simplified hot-pressing method [2]. The choice of specific additives may be a successful route to enhance magnetic properties [3]. This study shows the possibility of reaching a coercivity exceeding 2.5 kOe (200 kA/m) for 1 at.% Mo- and Cr-doped MnAlC powder and 3.3 kOe (263 kA/m) for V-doped MnAlC powder. This has been possible by combining gas-atomization and the self-developed flash-milling method (30-240 s) for efficient nanostructuring and promoting the creation of nanoprecipitates acting as pining centers [4]. A five-fold increase in coercivity has been achieved by comparison with that of the unmilled powder (see Fig. 2 for Mo-doped MnAlC). Furthermore, a proper choice of the milling time followed by an optimized annealing has allowed for combining high coercivity with an enhanced remanence (35 emu/g for a Cr-doped MnAlC sample) [4]. This approach opens a new path for engineering novel MnAlC doped nanostructures with promising PM properties. Acknowledgments. Gas-atomized powder was synthesized by Höganäs AB under the industrial project ECNanoManga between Höganäs and IMDEA Nanociencia. IMDEA acknowledges financial support by NEXUS project (PID2020-115215RB-C21) from MICINN.


![](https://assets.underline.io/uploads/markdown_image/1/image/405da192b48636c20674a5c79f4d28da.jpg)

![](https://assets.underline.io/uploads/markdown_image/1/image/1c8762f8591e2521a169282b95770c06.jpg)


Effect of Dopants (Mo, Cr, V) on the Magnetic Properties of Mn-Al-C nanostructured by Flash-Milling

Effect of Dopants (Mo, Cr, V) on the Magnetic Properties of Mn-Al-C nanostructured by Flash-Milling

Neodymium-based magnets are used dominantly in the industry due to their exceptional magnetic properties. However, because of regulations and environmental harm on rare earth elements, it is unsustainable to use Nd-Fe-B. Fe16N2 is proposed as an alternative to rare-earth-based magnets, as it shows a giant magnetic energy product and abundance of its elements. Here we demonstrate an improvement to our previously published low-cost synthesis method to produce highly coercive Fe16N2 flakes and a consolidation method to form it into a permanent magnet. The synthesis path begins with deforming iron powder into iron flakes by surfactant-assisted ball milling. Iron flakes are heat treated under air to achieve a porous morphology to increase Fe to Fe16N2 conversion yield. Porous flakes are reduced under Ar/H2 gas flow, followed by a low-temperature nitridation process under ammonia gas. Synthesized Fe16N2 flakes exhibit saturation magnetization up to 180 emu/g and coercivity up to 1.1 kOe. (Fig .1) Rietveld analysis of the X-ray diffraction measurement of flakes shows up to 93% volumetric fraction of Fe16N2 phase. To consolidate Fe16N2 cold press method is used. Consolidated flakes do not indicate any trace of phase decomposition, hence a solid Fe16N2 magnet is produced. (Fig.2.) A cost-effective method to bulk produce Fe16N2 magnet could be sustainable for next-generation magnet applications.

![](https://assets.underline.io/uploads/markdown_image/1/image/7ddd89cc469ea3d817f2c1579f38fe63.jpg)

![](https://assets.underline.io/uploads/markdown_image/1/image/32a762515db256c1caccd2c387137c01.jpg)

Fe16N2 Permanent Magnet Production by High-Pressure Consolidation

Magnetic properties and phase transformations in the archetypal binary alloys Fe-Pt, Co-Pt, and Fe-Pd are typically studied at near-equimolar compositions, due to the high magnetocrystalline anisotropy of the ordered L10 intermetallic. But these systems also possess eutectoid triple points, and proper thermal treatments at these compositions can create fascinating two-phase microstructures, e.g., nanochessboards in Co-Pt. Phase transformation behavior in the Fe-Pt system associated with the Fe-rich A1-&gt; L12+L10 eutectoid has barely been examined. We have produced an Fe-Pt arc melt with 34 at% Pt, nominally in the L12+L10 coexistence region. Continuous cooling of this sample through the eutectoid at various rates decomposes the high-temperature A1 phase into two tetragonal phases with different c/a ratios, rather than forming a cubic and tetragonal phase as suggested by the equilibrium phase diagram. Analysis of the Bragg-Williams long-range order parameter leads us to hypothesize the coexistence of L10 (Fig. 1) with the L1’ (Fig. 2) phase that was proposed by Shockley1in 1938. Subsequently, L1’ has been shown using computational approaches to be a stable low-temperature ordering of off-stoichiometry L10. L1’ is a specially decorated L10 lattice that accommodates off-stoichiometric compositions only on the basal-plane center atom. Until recent work by our group in Fe-Pd thin films, L1’ had not been observed experimentally. This research will examine the ordering mechanisms and phase evolution in bulk Fe-Pt, and the effect of ordering kinetics and lengthscales on the magnetic properties in and near the two-phase region. Support of the National Science Foundation through grant DMR-1709914 is gratefully acknowledged.

![](https://assets.underline.io/uploads/markdown_image/1/image/64f0d5ce5c5b7e547a65e0f74d3045cc.jpg)

Fig 1. In these unit cell illustrations, Fe is orange and Pt is gray. L10 and L1’ are both tetragonal phases that share the P4/mmm space group, however, the two structures accommodate (off-stoichiometric) excess iron differently. In our Fe- 34 at% Pt composition sample, fully ordered L10 distributes excess Fe-atoms equally across all Pt sites.

![](https://assets.underline.io/uploads/markdown_image/1/image/bc2a55a1cc1c177ae65a7d30f1de8720.jpg)

Fig 2. For the same composition, fully ordered L1’ places excess Fe-atoms only on the basal-plane center atom, while the corner Pt-site remains undisturbed.

The Formation of a Nanoscale Hard Magnetic Ferrite from Prussian Blue Nanocrystals

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The Formation of a Nanoscale Hard Magnetic Ferrite from Prussian Blue Nanocrystals

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