Magnetic Microstructure Research Articles

Vacuum processing temperature effect on highly coercive recycled NdFeB permanent magnets with Pr-based alloy addition

This study presents a modified method for recycling NdFeB scrap magnets, producing up to 100 kg of recycled sintered NdFeB magnets per batch. By adding a Pr-based alloy to N40H-grade NdFeB scrap and optimizing vacuum sintering and heat treatment conditions, we enhanced the magnetic properties and corrosion resistance of the recycled magnets. Various analyses, including BH Tracer measurements, FE-EPMA, accelerated corrosion tests, and C/N/O content analysis, evaluated differences in magnetic properties, microstructure, corrosion resistance, and impurity content. Optimal recycling involved vacuum sintering at 1085 °C, followed by heat treatments at 900 °C and 470 °C. Recycled magnets with PrCoGa alloy showed superior properties, such as an intrinsic coercivity (iHc) of 1414 kA/m, remanence (Br) of 1.290 T, and a maximum magnetic energy product ((BH)max) of 315.4 kJ/m, meeting N40H standards. Accelerated corrosion tests also indicated enhanced corrosion resistance in recycled magnets with Pr90Co8Ga2 alloy. This research offers a commercially viable approach for NdFeB magnet and rare earth element recycling.

Effect of Cobalt on the Microstructure of Fe-B-Sn Amorphous Metallic Alloys

Fe78B15Sn7 and (Fe3Co1)78B15Sn7 amorphous metallic alloys were prepared using the method of planar flow casting. The amorphous nature of ribbons containing 7 at. % Sn was verified by X-ray diffraction. The resulting chemical composition was checked by flame atomic absorption spectroscopy and by mass spectrometry with inductively coupled plasma. The microstructure of the as-quenched metallic glasses was investigated by 57-Fe and 119-Sn Mössbauer spectrometry. The experiments were performed with transmission geometry at 300 K, 100 K, and 4.2 K, and in an external magnetic field of 6 T. The replacement of a quarter of the Fe by Co did not cause significant modifications of the hyperfine interactions in the 57-Fe nuclei. The observed minor variations in the local magnetic microstructure were attributed to alterations in the topological short-range order. However, the in-field 57-Fe Mössbauer spectra indicated a misalignment of the partial magnetic moments. On the other hand, the presence of Co considerably affected the local magnetic microstructure of the 119-Sn nuclei. This was probably due to the higher magnetic moment of Co, which induces transfer fields and polarization effects on the diamagnetic Sn atoms.

Magnetic properties and microstructure of Ti-doped Sm-Fe-N synthesized by reduction diffusion process

Iron-rich intermetallic compound Sm2Fe17N3 is considered to be a highly promising candidate for new-generation permanent magnetic materials. Here, the Ti-substituted Sm2(Fe, Ti)17N3 alloys were synthesized using reduction-diffusion and nitridation. The microstructure and magnetic properties of Sm2(Fe, Ti)17 and its nitrides, in relation to the effect of Ti substitution, were systematically investigated through a comprehensive experimental approach combined with first-principles calculations. It was revealed that the Ti substitution is very effective in particle refinement of Sm2(Fe, Ti)17. The Rietveld analysis of X-ray data demonstrated an expansion in the unit cell volume of Sm2(Fe, Ti)17 phase with increasing Ti content. Subsequent nitridation experiments highlighted the beneficial impact of an appropriate Ti addition on the enhancement of both coercivity and remanence in Sm2(Fe, Ti)17N3 magnetic powder. The highest coercivity of 8.9 kOe was achieved in the sample with a Ti/Fe mole ratio of 0.04. Furthermore, the possible crystallographic occupancy of Ti and its effect on the phase stability are investigated using first-principles calculations. Our results indicated that the phase stability is influenced by the synergistic effect of Ti substitution atoms and interstitial N atoms. The significance of this study lies in its implications for the development of advanced permanent magnetic materials through reduction-diffusion technology.

Synergistic influence mechanism of B-Ga content on microstructures and magnetic properties of Nd-Fe-B ribbons

To understand the influence mechanism of B and Ga content on magnetic properties of NdFeB ribbons, Nd29.89FebalGayCo5.93Bx (wt%, x = 0.80–0.98, y = 0.24–1.04) alloys were prepared and magnetic properties, phase composition, coercivity mechanism, and microstructure of these alloys were investigated systematically. The melt-spun ribbons exhibited 2:14:1 phase grains with varying grain sizes and amorphous grain boundary phases at a wheel speed of 25 m/s. By reducing the B content within a specific range, grain refinement was achieved, resulting in narrower triangular grain boundaries, more uniform and continuous thin grain boundaries. Meanwhile, further increasing the Ga content, the grain shape changes from elongated to equiaxed, and the grain size is greatly refined. However, for x = 0.89, y = 0.84 strip, the coercivity is still reduced due to the large number of directly contacted grains. Consequently, an alloy composition of Nd29.89FebalGa0.64Co5.93B0.89 yielded excellent comprehensive magnetic properties, including a remanence of 8.5 kGs and a coercivity of 18.01 kOe. The corresponding magnetic properties enhancement mechanism is further discussed.

Optimizing color enhancement in dried Penaeus vannamei through high-humidity hot air impingement cooking: Enzyme inactivation, reduced drying time, and Maillard reaction inhibition

This study was aimed to evaluate the potential of high-humidity hot air impingement cooking (HHAIC) on Penaeus vannamei, focusing on its drying characteristics, microstructure, water distribution, enzyme activity, astaxanthin content, antioxidant capacity, color, and Maillard reaction. Results demonstrated that a 3 min HHAIC significantly improved the shrimp's color and optimized astaxanthin content with a notable increase in scavenging capacity based on an in-vitro as antioxidation activity evaluation. Compared to the untreated samples, HHAIC could significantly inactivate polyphenol oxidase by 95.76%. Also, it suppressed the Maillard reaction by decreasing 5-hydroxymethylfurfural content and shortened the drying time by 40%. In addition, the low-field nuclear magnetic resonance and microstructure analysis showed alterations in the shrimp muscle fiber structure and water distribution. This study indicated that HHAIC could elevate quality, enhance appearance, and reduce the processing time of dried shrimp, presenting valuable implications for industry progress.

Magnetic domain structures in ultrathin Bi2Te3/CrTe2 heterostructures

Abstract Chromium tellurium compounds are important two-dimensional van der Waals ferromagnetic materials with high Curie temperature and chemical stability in air, which is promising for applications in spintronic devices. Here, high-quality spin-orbital-torque (SOT) device, Bi2Te3/CrTe2 heterostructure was epitaxially grown on Al2O3 (0001) substrates. Anomalous Hall measurements indicate the existence of strong ferromagnetism in this device with the CrTe2 thickness down to 10 nm. In order to investigate its micromagnetic structure, cryogenic magnetic force microscope (MFM) was utilized to measure the magnetic domain evolutions at various temperatures and magnetic fields. The virgin domain state of the device shows a worm-like magnetic domain structure with the size around 0.6 ~ 0.8 µm. Larger irregular-shape magnetic domains (＞1µm) can be induced and pinned, after the field is increased to coercive field and ramped back to low fields. The temperature-dependent MFM signals exhibit a nice mean-field-like ferromagnetic transition with Curie temperature around 201.5 K, indicating a robust ferromagnetic ordering. Such device can be potentially implemented in future magnetic memory technology.

Elevated temperature magnetic microstructures and demagnetization mechanism for grain boundary diffused dual-main-phase (Nd, Ce)-Fe-B magnets

The combination of dual-main-phase (DMP) (Nd, Ce)-Fe-B magnets and grain boundary diffusion process (GBDP) is currently a research topic for obtaining high-cost performance materials in rare earth permanent magnet fields. The novel structural features of GBDP (Nd, Ce)-Fe-B magnets give a version of different domain reversal processes from those of non-diffused magnets. In this work, the in-situ magnetic domain evolution of the DMP magnets was observed at elevated temperatures, and the temperature demagnetization and coercivity mechanism of the GBDP dual-main-phase (Nd, Ce)-Fe-B magnets are discussed. The results show that the shell composition of different types of grains in DMP magnets is similar, while the magnetic microstructure results indicate the Ce-rich grains tend to demagnetize first. Dy-rich shell with a high anisotropic field caused by GBDP leads to an increase in the nucleation field, which enhances the coercivity. It is found that much more grains exhibit single domain characteristics in the remanent state for GBDP dual-main-phase (Nd, Ce)-Fe-B magnets. In addition, the grains that undergo demagnetization first are Ce-rich or Nd-rich grains, which is different from that of non-diffused magnets. These results were not found in previous studies but can be intuitively characterized from the perspective of magnetic domains in this work, providing a new perspective and understanding of the performance improvement of magnetic materials.

Nanofabrication, characterisation and modelling of soft-in-hard FeCo–FePt magnetic nanocomposites

Advanced nanofabrication exploiting e-beam lithography has been used to prepare nanocomposites consisting of periodic arrays of soft magnetic FeCo-based nano-inclusions of variable dimensions, embedded in a hard magnetic FePt matrix. Nanocomposites with non-magnetic (Pt) inclusions and single phase hard magnetic FePt microstructures were prepared as reference samples. The formation of Kirkendall voids in the soft-in-hard nanocomposites, because of annealing-induced diffusion, has been identified through high resolution imaging and chemical analysis. Replication of the μm-scaled nanocomposite and hard magnetic units over mm-scaled surfaces allowed global magnetic characterisation of magnetisation reversal using standard magnetometry. Magnetic force microscopy imaging was used for spatially resolved magnetic characterisation in different remanent magnetic states. Both of these experimental techniques were used to study the influence of the size, volume content and nature of the nano-inclusions on magnetisation reversal. The well-defined geometry and nano-scaled size of the inclusions render these nanocomposites as model systems for micromagnetic simulations and very good agreement was achieved between measured and simulated magnetisation reversal curves. This accordance motivates future in-silico optimisation of such soft-in-hard nanocomposites, which may serve as model systems to guide the design of new high performance bulk magnets which are less dependent on critical elements.

Magnon-Skyrmion Hybrid Quantum Systems: Tailoring Interactions via Magnons.

Coherent and dissipative interactions between different quantum systems are essential for the construction of hybrid quantum systems and the investigation of novel quantum phenomena. Here, we propose and analyze a magnon-skyrmion hybrid quantum system, consisting of a micromagnet and nearby magnetic skyrmions. We predict a strong-coupling mechanism between the magnonic mode of the micromagnet and the quantized helicity degree of freedom of the skyrmion. We show that with this hybrid setup it is possible to induce magnon-mediated nonreciprocal interactions and responses between distant skyrmion qubits or between skyrmion qubits and other quantum systems like superconducting qubits. This work provides a quantum platform for the investigation of diverse quantum effects and quantum information processing with magnetic microstructures.

Coercivity enhancement and microstructure optimization of Nd-Fe-Co-B magnets by Dy70Al10Cu20 grain boundary diffusion

The effect of grain boundary diffusion on the magnetic properties and microstructure of Nd-Fe-Co-B sintered magnets is investigated using Dy70Al10Cu20 alloy as the diffusion source. After the secondary annealing of the Nd-Fe-Co-B sintered magnet (Hcj = 7.94 kOe), its coercivity is substantially increased to 13.10 kOe. Following post-diffusion annealing, the coercivity of the sintered magnet significantly increased to 20.86 kOe. Microstructure analysis revealed that after the second annealing, the main phase grains in the magnet were connected but lacked thin intergranular phases. The distribution of Co was uneven, with an abundance of soft magnetic phases rich in Co, which was not conducive to improving coercivity. After diffusion, Dy formed a shell structure with high magnetic crystal anisotropy on the outer side of the main phase grains, leading to a significant increase in coercivity. Al and Cu entered the interior of the magnet, reducing the melting point of the grain boundary phase and promoting the uniform distribution of Co through the flow of the liquid phase. A large amount of thin continuous intergranular phase is generated inside the magnet, which helps reduce the exchange coupling between hard magnetic grains. The experimental results indicate that the Dy-Al-Cu alloy can effectively enhance the grain boundary structure of Nd-Fe-Co-B magnets, reduce the abundance of Co-rich phases, and improve the coercivity of the magnet.

Second harmonic generation in structures with inhomogeneous magnetization distribution

The study of the interaction of laser radiation with ferromagnetic materials is not only an inexhaustible source of new effects, but also provides an opportunity to study magnetic media at the micro- and macroscale. This is especially important for the development of modern technologies to produce structures with fundamentally new magnetic and optical properties that can’t be observed in natural materials. The review presents the results of studies of nonlinear optical effects in ferromagnetic nano- and microstructures, as well as films of different compositions. The unique capabilities of nonlinear-optical diagnostics of anisotropic, vortex, exchange-biased magnetic structures, visualization of the micromagnetic structure of the surface layers of ferrite garnets, based both on the high sensitivity of the optical second harmonic generation method to the magnetic state of nanostructures and interfaces, and on the symmetry properties of high-order magnetizationinduced susceptibility tensor have been demonstrated.

Magnetic properties and microstructure of Ce and Zr synergetic stabilizing Ti-lean SmFe12-based strip-casting flakes

Recently ThMn12-type samarium iron alloys have been promising materials for permanent magnets. Due to the high abundance and low cost, Ce as a possible stabilizer can be introduced into ThMn12-type alloys. The effect of Ce doping on the magnetic moment and phase stability in Ti-lean (Ce,Sm,Zr)(Fe,Co,Ti)12 compounds were predicted by the first-principles calculations. The CexSm0.8-xZr0.2(Fe0.8Co0.2)11.5Ti0.5 (x = 0–0.8) alloys with ThMn12 structure were produced by strip-casting into flakes by a wheel speed of 1.5 m/s and annealed at 1000 °C for 24 h. The Ce0.8Zr0.2(Fe0.8Co0.2)11.5Ti0.5 annealed flake shows a high saturation magnetization value of 13.6 kGs at room temperature. With the increase of Ce substitution in the annealed flakes, the content of α-(Fe,Co,Ti) phase decreases and the saturation magnetization increases. The 1:12 phase and the 1:9 phase have an orientation relationship that can be expressed as [0 0 –1]1:12//[100]1:9 and (020)1:12//(010)1:9. Besides, annealing process promotes the formation of 1:12 phase transformed from 1:9 phase. Coercivity is expected to be improved by obtaining uniform microstructure and suppressing the formation of soft α-(Fe,Co,Ti) phase in the ThMn12-based alloys.

An Active Strategy Based on Different Droplet Removal Modes on Polydimethylsiloxane Magnetic Microstructures.

The efficient removal of droplets on solid surfaces holds significant importance in the field of fog collection, condensation heat transfer, and so on. However, on current typical surfaces, droplets are characterized by a passive and single removal mode, contingent on the traction force (e.g., capillary force, Laplace pressure, etc.) generated by the surface's physics and chemistry design, posing challenges for enhancing the efficiency of droplet removal. In this paper, an effective active strategy based on different removal modes is demonstrated on magnetic responsive polydimethylsiloxane (PDMS) superhydrophobic microplates (RM-MPSM). By regulating the parameters of microplates and droplet volume, different effective departure modes (top jumping and side departure) can be induced to facilitate the removal of droplets. Moreover, the removal volume of droplets through the side departure mode exhibits a significant reduction compared to that observed in the top jumping mode. The exceptional removal ability of RM-MPSM demonstrates adaptability to diverse functional applications: efficient fog collection, removal of condensation droplets and micro-particles. The efficient modes of droplet removal demonstrated in this work hold significant implications for broadening its application in many fields, such as droplet collection, heat transfer, and anti-icing.

Production of Permanent Magnets from Recycled NdFeB Powder with Powder Extrusion Moulding

In the last fifteen years, several groups have investigated metal injection moulding (MIM) of NdFeB powder to produce isotropic or anisotropic rare earth magnets of greater geometric complexity than that achieved by the conventional pressing and sintering approach. However, due to the powder’s high affinity for oxygen and carbon uptake, sufficient remanence and coercivity remains difficult. This article presents a novel approach to producing NdFeB magnets from recycled material using Powder Extrusion Moulding (PEM) in a continuous process. The process route uses powder obtained from recycling rare earth magnets through Hydrogen Processing of Magnetic Scrap (HPMS). This article presents the results of tailored powder processing, the production of mouldable feedstock based on a special binder system, and moulding with PEM to produce green and sintered parts. The magnetic properties and microstructures of debinded and sintered samples are presented and discussed, focusing on the influence of filling ratio and challenging processing conditions on interstitial content as well as density and magnetic properties.

Magnetron-Deposited FeTiB Films: From Structural Metastability to the Specific Magnetic State

Results of XRD and TEM studies of a metastable phase state in Fe73Ti5B19O3 and Fe55Ti16B27O2 films, which is formed upon magnetron deposition under preset conditions, and of the evolution of the state in the course of subsequent annealing at 500 °C for 1, 5, and 9 h and experimental data on the magnetic microstructure and magnetic properties are reported. The annealed films were found to be characterized by a nanocrystalline structure, which is represented by two crystalline phases, namely, the ferromagnetic solid solution αFe(Ti), and nonferromagnetic boride FenB. The Ti content in the films determines the grain size of the αFe(Ti) phase, whereas the content of B localized within the grain boundaries determines the ratio of the volume fractions of amorphous and nanocrystalline phases in the structure. In contrast to the ferromagnetic Fe73Ti5B19O3 films, the Fe55Ti16B27O2 films are superparamagnets both in the deposited state and after annealing at 500 °C for 1 and 5 h because of the higher volume fraction of the amorphous phase in the structure. The 9 h annealing of the Fe55Ti16B27O2 films transfers them into the ferromagnets owing to the development of the amorphous phase crystallization, increase in the content of nanocrystalline ferromagnetic phase αFe(Ti) grains, and realization of exchange interaction between them.

Temperature-dependent evolution of micromagnetic structure of B20-type Fe1-xCoxGe studied by Mössbauer spectroscopy

The non-collinear magnetic structures hosted in magnets with broken central inversion symmetry, some of which are topologically non-trivial, have unique physical properties and application prospects. This paper presents a detailed study of the temperature evolution of the micromagnetic structures of B20-type Fe1-xCoxGe (x = 0, 0.05, 0.10) polycrystalline samples using 57Fe Mössbauer spectroscopy. We take the relatively weak electric quadrupole interaction as a perturbation of the hyperfine magnetic interaction to obtain the distribution of the hyperfine magnetic field Hhf (φ) in the plane perpendicular to the magnetic propagation vector ks. It is found that the geometric features of Hhf (φ) are sensitive to the relative orientation of ks regarding the electric field gradient at the iron nucleus, as well as to the spin texture. The temperature dependence of Hhf (φ) provides a distinct signal of first-order phase transition when ks shifts from [100] to [111]. The doping of cobalt atoms leads to out-of-plane component and in-plane component aggregation of the neighboring iron magnetic moments. These results are instructive for understanding the dynamical behavior of spiral magnets with long-periods.

Magnetic Properties, Phase Evolution, and Microstructure of Fe90Nb10 Powder Mixtures

Magnetic Properties, Phase Evolution, and Microstructure of Fe90Nb10 Powder Mixtures

Exploring the influence of anisotropy and microstructure of the sintered Nd-Fe-B magnet using nanoindentation and scratching tests

This study evaluated the influence of magnetic anisotropy and microstructure on the mechanical properties and material removal mechanism of anisotropic sintered Nd-Fe-B magnet. Nanoindentation tests were performed to measure the hardness (H), elastic (Es) and shear (G) modulus on two faces and main phases of the Nd-Fe-B material. To understand the contribution of the Nd2Fe14B1 and Nd-rich phases on material removal mechanism, scratching tests were also employed in the present study. Results showed that the Nd-Fe-B exhibits magnetic anisotropy with a high degree of uniaxial texture. Fracture analysis on the parallel and perpendicular faces related to the c-axis revealed no difference in fracture mechanisms. The load-displacement curves indicated that there is similar elastoplastic deformations induced by the penetration of indenter on the analyzed faces. Although Nd-Fe-B exhibits high magnetic anisotropy, the mechanical properties obtained from the two faces studied had not statistic difference. Nd-Fe-B is composed of hard and soft phases, where the Nd2Fe14B1 grain exhibited H = 12.5 ± 0.5 GPa, Es = 191.6 ± 12.6 and G = 77.3 ± 5.1 GPa, whereas the Nd-rich phase had values of H = 6.5 ± 0.7 GPa, Es = 124.0 ± 12.3 GPa and G = 50.0 ± 4.8 GPa. The Nd2Fe14B1 and Nd-rich phases strongly influenced scratch groove formation, being observed intergranular microcrack, replacement of Nd2Fe14B1 grain and bulging of Nd-rich grain boundaries. The mechanical properties of the Nd-Fe-B magnet were not affected by magnetic anisotropy or the high degree of uniaxial texture. However, the Nd2Fe14B1 grain presents higher hardness, elastic and shear modulus than the Nd-rich phase. Such characteristics can affect the machined surface formation when employing abrasive machining processes.

Soft magnetic properties, microstructure, and growth mechanism of FeSiAl soft magnetic powder cores fabricated via hexafluozirconic acid passivation

Soft magnetic properties, microstructure, and growth mechanism of FeSiAl soft magnetic powder cores fabricated via hexafluozirconic acid passivation

The Larmor frequency shift of a white matter magnetic microstructure model with multiple sources.

Magnetic susceptibility imaging may provide valuable information about chemical composition and microstructural organization of tissue. However, its estimation from the MRI signal phase is particularly difficult as it is sensitive to magnetic tissue properties ranging from the molecular to the macroscopic scale. The MRI Larmor frequency shift measured in white matter (WM) tissue depends on the myelinated axons and other magnetizable sources such as iron-filled ferritin. We have previously derived the Larmor frequency shift arising from a dense medium of cylinders with scalar susceptibility and arbitrary orientation dispersion. Here, we extend our model to include microscopic WM susceptibility anisotropy as well as spherical inclusions with scalar susceptibility to represent subcellular structures, biologically stored iron, and so forth. We validate our analytical results with computer simulations and investigate the feasibility of estimating susceptibility using simple iterative linear least squares without regularization or preconditioning. This is done in a digital brain phantom synthesized from diffusion MRI measurements of an ex vivo mouse brain at ultra-high field.