United States

Additive manufacturing (AM) of composites is attracting much interest in high-tech sectors for fabricating complex high-performance objects with tailored properties [1]. For permanent magnets (PMs), the challenge is to develop magnets by AM with no geometrical restrictions, high filling factor (FF), and non-deteriorated PM properties [2], together with finding alternatives (e.g., improved ferrites and promising MnAlC-based alloys) to rare earth-based magnets [3].&lt;br/&gt;Composites (PM particles/polymer) were synthesized by solution casting, followed by extrusion of filaments for 3D-printing, being reported for the very first time (Fig. 1). Several alternative PM materials were studied (gas-atomized τ-MnAlC, Sr-ferrite and hybrids —Sr-ferrite/NdFeB). Particle size and fine-to-coarse particles ratio (FP/CP) play a key role on the flexibility and powder loading of MnAlC filaments (length&amp;gt;10 m), reaching FF&amp;gt;80% and non-deteriorated PMs properties (Fig. 1) [4]. These results will be compared to the obtained for filaments based on Sr-ferrite (Hc=239 kA/m, FF=92%), NdFeB (Hc=812 kA/m, FF=93%) and hybrids (Hc=629 kA/m, FF=90%) (Fig. 2). MnAlC-based objects were 3D-printed under controlled temperature, proving that alternative PM materials can be efficiently synthesized and processed to develop novel PMs by AM (Fig. 1) [4].&lt;br/&gt;&lt;br/&gt;Acknowledgements. Authors acknowledge collaborations with B. Skårman, H. Vidarsson and P.-O. Larsson (Höganäs, Sweden) by the industrial contract &lt;i&gt;GAMMA,&lt;/i&gt; and A. Nieto and R. Altimira (IMA, Spain), and financial support from: EU M-ERA.NET by &lt;i&gt;COSMAG&lt;/i&gt; project (PCI2020-112143); MICINN by &lt;i&gt;NEXUS&lt;/i&gt; project (PID2020-115215RB-C21); CM by &lt;i&gt;NanoMagCOST&lt;/i&gt; project (P2018/NMT-4321).

![](https://assets.underline.io/uploads/markdown_image/1/image/3da8e2e0919c7ea3ed6b01fc3af543f4.jpg)

Fig. 1. (a) Gas-atomized MnAlC, polymer, and composite; (b) SEM image of MnAlC particles and size distribution; (c), (d) image and SEM cross section of a MnAlC/ABS filament; (e) MnAlC-based 3D-printed object; (f) normalized magnetic response of MnAlC-based samples; and (g) magnetic flux density of a 3D-printed MnAlC-based disc.


![](https://assets.underline.io/uploads/markdown_image/1/image/b00d3d1a8d0386d3ac76cfe5a8bfe75e.jpg)

Fig. 2. (a) SEM and EDX of a hybrid composite; (b) second quadrant of the hysteresis loops for the hybrid, Sr ferrite- and NdFeB-based materials. Insets show composite pellets and SEM cross section of a Sr ferrite-based filament.

2022 Joint MMM-INTERMAG

Optimizing the Particle Size Distribution in Permanent Magnet Composites to Extrude Flexible Filaments for Additive Manufacturing

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.

The 2022 Joint Conference will offer both in-person and prerecorded on-demand content.

For tickets to the event, please register at the following link: https://magnetism.org/register

Please register for the Joint MMM-Intermag conference to join the event.

This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

Additive manufacturing (AM) of composites is attracting much interest in high-tech sectors for fabricating complex high-performance objects with tailored properties [1]. For permanent magnets (PMs), the challenge is to develop magnets by AM with no geometrical restrictions, high filling factor (FF), and non-deteriorated PM properties [2], together with finding alternatives (e.g., improved ferrites and promising MnAlC-based alloys) to rare earth-based magnets [3]. Composites (PM particles/polymer) were synthesized by solution casting, followed by extrusion of filaments for 3D-printing, being reported for the very first time (Fig. 1). Several alternative PM materials were studied (gas-atomized τ-MnAlC, Sr-ferrite and hybrids —Sr-ferrite/NdFeB). Particle size and fine-to-coarse particles ratio (FP/CP) play a key role on the flexibility and powder loading of MnAlC filaments (length&gt;10 m), reaching FF&gt;80% and non-deteriorated PMs properties (Fig. 1) [4]. These results will be compared to the obtained for filaments based on Sr-ferrite (Hc=239 kA/m, FF=92%), NdFeB (Hc=812 kA/m, FF=93%) and hybrids (Hc=629 kA/m, FF=90%) (Fig. 2). MnAlC-based objects were 3D-printed under controlled temperature, proving that alternative PM materials can be efficiently synthesized and processed to develop novel PMs by AM (Fig. 1) [4]. Acknowledgements. Authors acknowledge collaborations with B. Skårman, H. Vidarsson and P.-O. Larsson (Höganäs, Sweden) by the industrial contract GAMMA, and A. Nieto and R. Altimira (IMA, Spain), and financial support from: EU M-ERA.NET by COSMAG project (PCI2020-112143); MICINN by NEXUS project (PID2020-115215RB-C21); CM by NanoMagCOST project (P2018/NMT-4321).

![](https://assets.underline.io/uploads/markdown_image/1/image/3da8e2e0919c7ea3ed6b01fc3af543f4.jpg)

Fig. 1. (a) Gas-atomized MnAlC, polymer, and composite; (b) SEM image of MnAlC particles and size distribution; (c), (d) image and SEM cross section of a MnAlC/ABS filament; (e) MnAlC-based 3D-printed object; (f) normalized magnetic response of MnAlC-based samples; and (g) magnetic flux density of a 3D-printed MnAlC-based disc.


![](https://assets.underline.io/uploads/markdown_image/1/image/b00d3d1a8d0386d3ac76cfe5a8bfe75e.jpg)

Fig. 2. (a) SEM and EDX of a hybrid composite; (b) second quadrant of the hysteresis loops for the hybrid, Sr ferrite- and NdFeB-based materials. Insets show composite pellets and SEM cross section of a Sr ferrite-based filament.

technical paper

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.

Indications for Novel L1’ Ordering in Fe-Pt Alloys Near the Fe-rich Eutectoid Composition

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

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

M-type hexaferrites is known to be sensitive to thier chemical composition, which can be an effective instrument to preciesly control magnetic properties of the materials. In this study, we demonstrate the synthesis and the investigation of the magnetostatic and magnetodynamic properties of single-domain gallium substituted strontium M-type hexaferrite particles SrFe12-xGaxO19 (x = 1 - 6). The synthetic approach is based on a precursor preparation via a facile citrate-nitrate auto-combusion method followed by thermal treatment at 1200 oC. The annealing of the porous precursor led to the formation of single-domain hexaferrite particles with mean sizes of 360 – 560 nm. Introduction of Ga3+ ions up to x = 4 into the hexaferrite structure resulted in a growth of coercivity from 5.1 to 6.4 kOe, and further increase in gallium concentration led to a decrease in the coercivity. The samples display natural ferromagnetic resonance frequency in the range of 49 – 57 GHz. Crystal structure refinement reveals, that Ga3+ ions preferably occupy 2a, 4f1, 12k, and 2b sites and cause a decrease in the magnetic anisotropy and a modest decrease in the saturation magnetization. The research was supported by RFBR grant no 21-53-12002.

![](https://assets.underline.io/uploads/markdown_image/1/image/6afe94576952d0d11bb2fe1d826dc0da.jpg)

a) Magnetic hysteresis loops of SrFe12-xGaxO19 (x = 0 – 6) samples; b) The dependencies on the substitution degree (x) of coercivity (HC) and saturation magnetization (MS).

Submicron particles of Ga-substituted strontium hexaferrite obtained by citrate auto-combustion method

Ferrites are the most used permanent magnets (PMs) due to their availability and low cost, being an alternative to PMs based on critical rare-earths in new applications such as electromobility [1]. In this work we will show the possibility of 3D-printing objects using strontium ferrite powder obtained by successful recycling of the residue generated from manufacturing commercial ferrite magnets. Tuning the morphology and microstructure of the Sr-ferrite residue by post-processing made possible to end with Sr-ferrite powder with PM properties superior, not only to the residue precursor, but to those of the brand new commercial powder (3.5 fold increase in coercivity and a 25% increase in remanence) [2]. The recycled ferrite was used as precursor for synthesizing composites by the solution casting method [3], and extruding filaments for advanced manufacturing of magnets (with a particle content up to 65 wt%) by Fused Filament Fabrication. Magnetic characterization of composites, filaments and printed objects was performed by Vibrating Sample Magnetometer (VSM), showing that the magnetization scales accordingly to the content of ferrite particles and that there is no deterioration of the PM properties of the starting particles along processing (Fig. 1). Scanning Electron Microscopy (SEM) analysis showed a homogeneous distribution of the particles in the polymer matrix (Fig. 2) [4]. This work has shown an efficient path for developing new and alternative PMs by the combination of recycling and 3D-printing. Acknowledgements. Authors acknowledge financial support from MICINN by NEXUS project (PID2020-115215RB-C21), industrial collaboration PLASMAG with IMA S.L.U. and from the Regional Government of Madrid by NanoMagCOST project (P2018/NMT-4321).

![](https://assets.underline.io/uploads/markdown_image/1/image/ac2f3c775797ab289c0ec1e59559f011.jpg)

Fig. 1. (a) First and second quadrants of the hysteresis loops of starting powder and composites with different content of ferrite. (b) Normalized hysteresis loops of the starting powder, composite and 3D-printed object. Insets show a 3D-printed piece based on ferrite particles.

![](https://assets.underline.io/uploads/markdown_image/1/image/ce076f52b81f87799a6418acd5c64cfb.jpg)

Fig. 2. SEM images of: (a) cross section and (b) closer view of a magnetic filament with a 50 wt% of ferrite; and (c) and (d) inner morphology of a 3D-printed object with a particle content of 65 wt%.

Optimizing the Particle Size Distribution in Permanent Magnet Composites to Extrude Flexible Filaments for Additive Manufacturing

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Optimizing the Particle Size Distribution in Permanent Magnet Composites to Extrude Flexible Filaments for Additive Manufacturing

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