Fabrication Of Permanent Magnets Research Articles

Optimized Route for the Fabrication of MnAlC Permanent Magnets by Arc Melting

The rare-earth-free MnAlC alloy is currently considered a very promising candidate for permanent magnet applications due to its high anisotropy field and relatively high saturation magnetization and Curie temperature, besides being a low-cost material. In this work, we presented a simple fabrication route that allows for obtaining a magnetically enhanced bulk τ-MnAlC magnet. In the fabrication process, an electric arc-melting method was carried out to melt ingots of MnAlC alloys. A two-step solution treatment at 1200 °C and 1100 °C allowed us to synthesize a pure room-temperature ε-MnAlC ingot that completely transformed into τ-MnAlC alloy, free of secondary phases, after an annealing treatment at 550 °C for 30 min. The Rietveld refinements and magnetization measurements demonstrated that the quenched process produces a phase-segregated ε-MnAlC alloy that is formed by two types of ε-phases due to local fluctuation of the Mn. Room-temperature hysteresis loops showed that our improved τ-MnAlC alloy exhibited a remanent magnetization of 42 Am2/kg, a coercive field of 0.2 T and a maximum energy product, (BH)max, of 6.07 kJ/m3, which is higher than those reported in previous works using a similar preparation route. Experimental evidence demonstrated that the synthesis of a pure room-temperature ε-MnAlC played an important role in the suppression of undesirable phases that deteriorate the permanent magnet properties of the τ-MnAlC. Finally, magnetic images recorded by Lorentz microscopy allowed us to observe the microstructure and magnetic domain walls of the optimized τ-MnAlC. The presence of magnetic contrasts in all the observed grains allowed us to confirm the high-quality ferromagnetic behavior of the system.

Annealing effect on microstructure and magnetic properties of nanocrystalline Zr6Fe23 compound

In this work, we studied annealing effect on microstructure and magnetic properties of nanocrystalline Zr6Fe23 powders prepared by high-energy ball milling. The Zr6Fe23 compound crystallize in a cubic phase of Th6Mn23 type structure (Fm-3 m space group). The annealed Zr6Fe23 samples exhibit a strong temperature dependence of the extrinsic properties. The relationship between the morphology, grains size and magnetic anisotropy properties was analyzed. The significant improvement of coercivity Hc, remanent magnetization Mr and maximum energy product (BH)max is due to the finer grains of the samples. The nanocrystalline Zr6Fe23 compound annealed at Ta = 1325 K exhibits the best magnetic properties, having Hc of 3759 Oe, Mr = 71 emu/g, (BH)max = 1.2 MGOe, Curie temperature TC≃ 821 K and magnetic anisotropy field Ha = 26403 Oe. The results of this work could potentially open the way for future exploration and fabrication of permanent magnets or spintronic devices from nanocrystalline Zr6Fe23 alloys.

Microstructure and magnetic properties of Nd-Fe-B permanent magnets produced by laser powder bed fusion

Additive manufacturing of Nd-Fe-B is a novel approach for the fabrication of permanent magnets. We present an analysis of the magnetic properties and microstructure of Nd-Fe-B permanent magnets, which were produced by laser powder bed fusion (LPBF). By optimization of processing parameters for the Nd-lean powder coercivity of 921 kA/m (1.16 T), remanence of 0.63 T and maximum energy product of 63 kJ/m3 are achieved without the addition of further Nd-rich low-melting alloys or any other post treatment. Thereby, remanence and maximum energy product represent the highest reported values for additively manufactured permanent magnets. The impact of area energy density EA on the magnetic properties is discussed. The isotropic microstructure consists of short Nd2Fe14B dendrites at the melt pool boundaries and globular sub-micron sized grains in the melt pool interior. After LPBF of the Nd-lean powder no evidence of α-Fe is found in the microstructure.

Magnetophoresis-Assisted Capillary Assembly: A Versatile Approach for Fabricating Tailored 3D Magnetic Supercrystals.

The fabrication and integration of sub-millimeter magnetic materials into predefined circuits is of major importance for the realization of portable devices designed for telecommunications, automotive, biomedical, and space applications but remains highly challenging. We report here a versatile approach for the fabrication and direct integration of nanostructured magnetic materials of controlled shaped at specific locations onto silicon substrates. The magnetophoresis-assisted capillary assembly of magnetic nanoparticles, either spherical or anisotropic, leads to the fabrication of high-performance Co-based permanent magnets and Fe-based supercrystals. Integrated sub-millimeter magnets as well as millimeter self-standing magnets exhibiting magnetic properties competing with NdFeB-based composites were obtained through this cost- and time-efficient process. The proof-of-concept of electromagnetic actuation of a micro-electromechanical system cantilever by means of these supercrystals highlights their potentiality as efficient integrated magnetic materials within nomadic devices.

Geometric effects in cylindrical core/shell hard–soft exchange-coupled magnetic nanostructures

We explore the optimal condition for cylindrical core/shell hard-soft exchange-coupled magnetic nanostructures by obtaining full hysteresis loops for various geometries by obtaining full hysteresis loops for various geometrical variables, including the dimensional scale and soft/hard-magnetic phase volume ratio through micromagnetic simulations. For achieving maximum energy product (BH), it is essential to increase the demagnetizing field by increasing the volume fraction of the soft magnet while maintaining a positive nucleation field and, which can be possible by the scaling-down. To scale up the nanostructure to a bulk magnet having high BH can be achieved by forming an array of needle-shaped exchange-coupled cylinders. These findings could lead to the flexible design and scalable fabrication of exchange-coupled permanent magnets.

A Study of the Microstructure and Magnetic Properties of Fe – Cr – Co Alloys with Reduced Content of Coobtained by the Mim Technology

The possibility of fabrication of permanent magnets based on a Fe – Cr – Co alloy with reduced cobalt content by the MIM technology is considered. The method is used to obtain permanent magnets 3 × 2 × 6 mm in size with magnetic properties close to those of standard 25Kh15KA magnets produced by investment casting. The microstructure and the magnetic properties of the alloys are studied.

Improvement of microstructure and coercivity for Nd-Fe-B sintered magnets by boundary introducing low melting point alloys

Different from the grain boundary diffusion process (GBDP), which is suitable for modifying thin magnet, a green-pressing agents permeation process (GAPP) that uses low melting point alloys was applied to the Nd-Fe-B green compact with a thickness over 15 mm to reconstruct the boundary microstructure of a sintered Nd-Fe-B magnet. The coercivity increases from 12.3 kOe for the sample free of Pr80Al20 to 16.8 kOe for the sample with 2 wt% Pr80Al20. By further increasing the Pr80Al20 content to 3 wt%, the coercivity increases slightly, but the remanence and Hk/Hcj deteriorate obviously. The optimal comprehensive properties of Hcj = 16.8 kOe, Br = 13.4 kG and Hk/Hcj = 0.975 are obtained at 2 wt% Pr80Al20, since matrix phase grains are separated by relatively continuous thin grain boundary layers, which weaken the magnetic coupling between adjacent grains. The coercivities of the samples from the GAPP that use 2 wt% Pr80Al20, Pr70Cu30 and Pr60Tb20Al20 alloys, respectively, can be enhanced to a large extent. However, the coercivity of the magnet reconstructed with Pr80Al20 is lower than that of the sample with Pr60Tb20Al20 but is higher than that of the sample reconstructed with Pr70Cu30 alloy. Moreover, the coercivity of the sample from the GAPP using 2 wt% Pr80Al20 is much higher than that of the sample from the GBDP, which is due to a nearly uniform boundary microstructure from the surface to the interior of the thick magnet from the GAPP, thus providing new insights into the fabrication of thick and bulky permanent magnets with high coercivity.

Chemical Synthesis of Magnetically Hard and Strong Rare Earth Metal Based Nanomagnets.

We report a general chemical approach to synthesize strongly ferromagnetic rare-earth metal (REM) based SmCo and SmFeN nanoparticles (NPs) with ultra-large coercivity. The synthesis started with the preparation of hexagonal CoO+Sm2 O3 (denoted as SmCo-O) multipods via decomposition of Sm(acac)3 and Co(acac)3 in oleylamine. These multipods were further reduced with Ca at 850 °C to form SmCo5 NPs with sizes tunable from 50 to 200 nm. The 200 nm SmCo5 NPs were dispersed in ethanol, and magnetically aligned in polyethylene glycol (PEG) matrix, yielding a PEG-SmCo5 NP composite with the room temperature coercivity (Hc ) of 49.2 kOe, the largest Hc among all ferromagnetic NPs ever reported, and saturated magnetic moment (Ms ) of 88.7 emu g-1 , the highest value reported for SmCo5 NPs. The method was extended to synthesize other ferromagnetic NPs of Sm2 Co17 , and, for the first time, of Sm2 Fe17 N3 NPs with Hc over 15 kOe and Ms reaching 127.9 emu g-1 . These REM based NPs are important magnetic building blocks for fabrication of high-performance permanent magnets, flexible magnets, and printable magnetic inks for energy and sensing applications.

Enhanced coercivity of Nd-Ce-Fe-B sintered magnets by adding (Nd, Pr)-H powders

Incorporating the highly abundant rare earth (RE) Ce into Nd-Fe-B sintered magnets has attracted considerable interest recently. The inferior anisotropic field (HA) of Ce2Fe14B to Nd2Fe14B, however leads to low coercivity of the Nd-Ce-Fe-B magnets. To further enhance the coercivity, in this work, (Nd, Pr)-H powders were used as intergranular additive to restructure the grain boundaries of the low cost (Nd,Pr)22.3Ce8.24FebalB1 (wt.%) sintered magnets. When added with only 2 wt% (Nd, Pr)-H, the Hcj can be enhanced from 10.6 kOe to 12.7 kOe with slight reduction in remanence and maximum energy product. The dehydrogenation of (Nd, Pr)-H during sintering promotes the diffusion of Nd and Pr towards the 2:14:1 phase grains and the smoothing of grain boundaries. The formation of (Nd, Pr)-rich shell with locally enhanced magnetocrystalline anisotropy and the magnetic isolation between adjacent 2:14:1 phase grains result in obvious coercivity enhancement, which was supported by magnetic domain structure characterizations and micromagnetic simulations. It suggests that through grain boundary restructuring, the coercivity of Nd-Ce-Fe-B magnets can be enhanced to be comparable of commercial Nd-Fe-B magnets, which may shed new insights into the fabrication of low cost RE permanent magnets.

Fabrication of bulk nanostructured permanent magnets with high energy density: challenges and approaches.

Nanostructured permanent magnetic materials, including exchange-coupled nanocomposite permanent magnets, are considered as the next generation of high-strength magnets for future applications in energy-saving and renewable energy technologies. However, fabrication of bulk nanostructured magnets remains very challenging because conventional compaction and sintering techniques cannot be used for nanostructured bulk material processing. In this paper we review recent efforts at producing bulk nanostructured single-phase and composite magnetic materials with emphasis on grain size control, anisotropy generation and interface modification.

Magneto-optical properties and Mössbauer Investigation of BaxSryPbzFe12O19 Hexaferrites

Ba0.3Sr0.4Pb0.3Fe12O19, Ba0.4Sr0.3Pb0.3Fe12O19 and Ba0.3Sr0.3Pb0.4Fe12O19 hexaferrites were synthesized via sol-gel auto combustion. XRD (X-ray powder diffraction) powder patterns of the products confirmed the formation of M-type hexaferrites without any secındary phase. The crystallite sizes of the products were calculated as 37–41nm by Scherrer equation. SEM (Scanning electron microscopy) analyses revelaed the hexagonal morphology and 200–400nm grain size of the prodcuts. The magnetic hysteresis (σ-H) curves exhibit the ferromagnetic features for all hexaferrites. Especially, Ba0.3Sr0.4Pb0.3Fe12O19 and Ba0.4Sr0.3Pb0.3Fe12O19 samples have suitable magnetic characteristics (saturation magnetizations as 42.58 and 38.55emu/g, coercive fields as 1950 and 2978Oe, larger squareness ratios (SQR) as 0.447 and 0.454, respectively) for high density magnetic recording applications and permanent magnet fabrication. Effective crystalline anisotropy constants (Keff) are between 3.18×105–3.54×105Erg/g. The observed 17000OeHa (anisotropy field) reveal that products are hard magnet. Tauc plots were plotted to determine the Eg (direct optical energy band gap) of the samples. The Eg values are 1.46, 1.51, 1.69eV belonging to Ba0.3Sr0.4Pb0.3Fe12O19, Ba0.4Sr0.3Pb0.3Fe12O19, and Ba0.3Sr0.3Pb0.4Fe12O19 hexaferrites respectively.

Fabrication and integration of microscale permanent magnets for particle separation in microfluidics

Microfluidic magnetophoresis is an effective technique to separate magnetically labeled bioconjugates in lab-on-a-chip applications. However, it is challenging and expensive to fabricate and integrate microscale permanent magnets into microfluidic devices with conventional methods that use thin-film deposition and lithography. Here, we propose and demonstrate a simple and low-cost technique to fabricate microscale permanent magnetic microstructures and integrate them into microfluidic devices. In this method, microstructure channels were fabricated next to a microfluidic channel and were injected with a liquid mixture of neodymium (NdFeB) powders and polydimethylsiloxane (PDMS). After the mixture was cured, the resulted solid NdFeB–PDMS microstructure was permanently magnetized to form microscale magnets. The microscale magnets generate strong magnetic forces capable of separating magnetic particles in microfluidic channels. Systematic experiments and numerical simulations were conducted to study the geometric effects of the microscale magnets. It was found that rectangular microscale magnets generate larger \(({\mathbf {H}}\cdot \nabla ) {\mathbf {H}}\) which is proportional to magnetic force and have a wider range of influence than the semicircle or triangle magnets. For multiple connected rectangular microscale magnet, additional geometric parameters, including separation distance, height and width of the individual elements, further influence the particle separation and were characterized experimentally. With an optimal size combination, complete separation of yeast cells and magnetic microparticles of similar sizes (\(4\;\upmu \hbox {m}\)) was demonstrated with the multi-rectangular magnet microfluidic device.

Experimental Proof of Microwave Sintering of Nd–Fe–B Powders Toward Fabrication of Permanent Magnets

The Nd-Fe-B magnets were prepared using conventional and microware sintering processes. A finely tuned microwave cavity operating in the 2.45 GHz, which works in single mode of electric field (e-field), was used to investigate the microwave sintering of Nd-Fe-B powders. The highest sintering temperature used was 1173 K, and the sintering lasted up to 610 s. The density of microwave sintered Nd-Fe-B magnets could reach values as high as 7.43 g/cc. We have managed to sinter Nd-Fe-B powders and produce magnets at a fraction of the time and energy used in conventional resistive/radiant heating, which is in excess of 1273 K for many hours, and in many cases after homogenization at high temperatures.

Optimization of the magnetic properties of aligned Co nanowires/polymer composites for the fabrication of permanent magnets

We aim at combining high coercivity magnetic nanowires in a polymer matrix in a view to fabricate rare-earth free bonded magnets. In particular, our aim is to fabricate anisotropic materials by aligning the wires in the polymer matrix. We have explored the different parameters of the fabrication process in order to produce a material with the best possible magnetic properties. We show that the choice of a proper solvent allows obtaining stable nanowire suspensions. The length and the type of the polymer chains play also an important role. Smaller chains (Mw < 10,000) provide better magnetization results. The magnetic field applied during the casting of the material plays also a role and should be of the order of a fraction of a tesla. The local order of the nanowires in the matrix has been characterized by TEM and small angle X-ray scattering. The correlation between the local order of the wires and the magnetic properties is discussed. Materials with coercivity μ0Hc up to 0.70 T at room temperature have been obtained.

Fabrication and Microstructure Evolution of Single Crystalline Sm2Co17 Nanoparticles Prepared by Mechanochemical Method

In this work we report fabrication and microstructural characterization of single crystalline Sm2Co17 nanoparticles with an average size of 103.7 nm. These particles are fabricated using mechanochemical method and can be used for fabrication of high performance permanent magnets due to their high coercivity (20 kOe). Microstructure analysis reveals the inhomogeneity and defects in the nanoparticles. The origin of these defects was analyzed and discussed by systematic microstructural investigation of the as-milled, annealed, and washed samples. On the basis of these results, by further optimizing the processing parameters, properties of the nanoparticles can be improved.

Resin-bonded NdFeB micromagnets for integration into electromagnetic vibration energy harvesters

A micromachining technique is presented for the fabrication of resin-bonded permanent magnets in the microscale. Magnetic paste is prepared from NdFeB powder and an epoxy resin, filled into lithographically defined photoresist molds or metal molds, and formed into resin-bonded magnets after curing at room temperature. A coercivity of 772.4 kA/m, a remanence of 0.27 T, and a maximum energy product of 22.6 kJ/m3 have been achieved in an NdFeB disk micromagnet with dimensions of Φ200 μm×70 μm. Based on the developed micro-patterning of resin-bonded magnets, a fully integrated electromagnetic vibration energy harvester has been designed and fabricated. The dimensions of the energy harvester are only 4.5 mm×4.5 mm×1.0 mm, and those of the micromagnet are 1.5 mm×1.5 mm×0.2 mm. This microfabrication technique can be used for producing permanent magnets tens or hundreds of micrometers in size for use in various magnetic devices.

De l’atelier au laboratoire: Recherche et innovation dans l’industrie électrique, XIX e –XX e siècles (review)

Reviewed by: De l’atelier au laboratoire: Recherche et innovation dans l’industrie électrique, XIXe–XXe siècles Andrew Butrica (bio) De l’atelier au laboratoire: Recherche et innovation dans l’industrie électrique, XIXe–XXe siècles. Edited by Yves Bouvier et al. Frankfurt am Main: Peter Lang, 2011. Pp. 141. $38.95. The goal of this slim installment in Peter Lang’s History of Energy series is to explore the nature and loci of electrical industry invention, innovation, research, and development and to challenge the accepted view of nineteenth-century lone inventor-geniuses and twentieth-century richly endowed corporate laboratories. It substantively broadens and deepens the work of Robert Fox and Anna Guagnini’s Laboratories, Workshops, and Sites: Concepts and Practices of Research in Industrial Europe, 1800–1914 (1999). The contributions represent revisions of half the papers read at a [End Page 933] December 2005 conference in Mulhouse, France, the other half appearing in a 2007 issue of Annales historiques de l’électricité. The authors of the six articles succeed superbly in relocating and redefining industrial research. W. Bernard Carlson, in a study of Nikola Tesla’s AC motor and wireless transmission of high-frequency power, argues the case for the inventor’s advantages over big firms, advantages that arise from being unhampered by the constraints of production and marketing. Tesla exemplified Joseph Schumpeter’s separation of invention and development by allying himself with promoters and selling or licensing his patents rather than establishing manufacturing plants. Alain Cortat analyzes Swiss cable-making firms in the context of a national (eventually international) cartel. Research and quality control evolved side-by-side until their separation during the 1930s. The firms overcame their small size and limited finances to innovate by purchasing patents from industrial groups (Bell, Siemens, Philips), collaborating with universities and technical schools, and contracting research with the Battelle Institute (1960s). Serge Paquier reminds the reader in a study of long-distance electrical power transmission that not all research took place indoors. Building up to the Frankfurt electrical exposition of 1891 (and so accenting the importance of these expositions for technological advance), Paquier focuses on hydroelectric installations as laboratories “hors les murs.” In an inquiry on the Toulouse electrical engineering laboratory (LGET), Marie-Pierre Bès calls attention to the critical role played by government policy and sponsorship in France between 1955 and 1985. The research carried out legitimated a nascent discipline in applied science and served the needs of industry (chiefly the electric monopoly EDF) with public underwriting largely from the Ministry of Industry and Research, the CNRS, and research agencies in the critical space, telecommunications, and nuclear sectors. The research never led to patents or the conception of new products or processes, but did fulfill the electrical industry’s strategic needs. Graeme Gooday revisits Marie Sklodowska Curie’s original contribution to the science and fabrication of permanent steel magnets (which too often proved to lack permanence), underwritten by the Société d’encouragement pour l’industrie nationale in the 1890s and carried out in the Sorbonne and École de physique et de chimie. His main attention is on the received notion in “narrow folklore” (p. 107) that Sydney Evershed in 1920 and 1925 solved the permanent magnet problem and established their manufacture on a scientific basis through decades of designing and redesigning electrical instruments. Here British trade secrecy collided with (and obscured) the results of Curie’s science-based open and systematic approach that relied on an assortment of samples donated by industry. Gabriel Galvez-Behar tackles Clément Ader, a telegraph, telephone, and automobile innovator too often associated solely with aeronautics. He [End Page 934] focuses on Ader’s changing contractual relationships with the Société générale des téléphones and the Société industrielle des téléphones to provide patentable inventions on demand. Ader successfully and simultaneously performed aeronautical research for the army because he operated as an “inventor entrepreneur” (like Edison) acting as both inventor (and insisting that his name be on all patents) and an entrepreneur who managed multiple research teams working on different problems (telephony, air transport, automobiles) at separate locations. A firm’s lack...

Anomalous Behavior of Chemically Synthesized Magnetoplumbite Strontium Ferrite Nano Particles

Strontium hexa-ferrite nanoparticles were prepared successfully by simple co-precipitation method. The XRD analysis confirmed the formation of single phase MFe12O19 (M=Sr). Parameters such as crystallite size, lattice constant, X-ray density and porosity were calculated from the X-ray diffraction data. The crystallite sizes were in the range 12-26 nm. The temperature dependent dc electrical resistivity measurements showed that the material was highly. Dielectric constant and dielectric loss factor (tanδ) were measured in the frequency range 20Hz-3MHz. The anomalous behavior of dielectric loss revealed a very important behavior of the prepared sample of SrFe12O19 in different frequency regions and that could be used for new applications of this material. The magnetic properties were determined from the hystersis loop obtained from vibrating sample magnetometer (VSM). The Curie temperature was determined by susceptometer. This material is potentially suitable for use as a recording medium in identification cards and credit cards and for the fabrication of permanent magnets.

EFFECT OF pH VALUE AND CALCINATION TEMPERATURE ON STRUCTURE AND MAGNETIC PROPERTIES OF STRONTIUM HEXAFERRITE THIN FILM

Strontium hexaferrite was widely used in the fabrication of commercial permanent magnets and certain microwave devices. In this study, the strontium hexaferrite nanoparticle coatings were prepared by sol–gel method and using spin coating process on silicon substrate, then the effect of pH value, such as 5, 7 and 9, and calcination temperatures, such as 600°C, 800°C, and 1000°C, on structural and magnetic properties of strontium hexaferrite thin films were investigated by XRD, SEM and VSM measurements. The maximum saturation magnetization value of 57.43 emu/g and coercivity value of 3908 Oe were achieved for the thin film with crystallite size approximately 41 nm, prepared at pH value of 7 and calcinations temperature of 800°C.

Thin films of NdFeB deposited by PLD technique

Neodymium–iron–boron (NdFeB) is a material with important magnetic properties, mostly used in permanent magnet fabrication. Thin layers of NdFeB are needed for miniaturization in electrical engineering, electronics and for high-tech devices. In this paper we applied pulsed lased deposition (PLD) in vacuum for obtaining thin films of NdFeB from stoichiometric targets. The influence of different buffer layers and of the laser parameters (wavelength and fluence) on the NdFeB structures, composition and magnetic properties have been investigated. The obtained structures were characterized by atomic force microscopy (AFM) and optical microscopy. Vibrating sample magnetometry (VSM) has been performed for specific magnetic characterization.