SmCo Magnets Research Articles

Ultra-high coercivity Sm-Co bulk magnets with remarkable thermal stability

The Sm-Co bulk magnet prepared in this work using unique Sm-Co alloy nanopowder as a precursor prepared by the lox oxygen-induction thermal plasma (LO-ITP) process displays a giant coercivity of 4.1 MA/m (52 kOe) at 300 K, which is the highest coercivity among the reported rare-earth permanent bulk magnets with high density. The Sm-Co magnet has a high coercivity of 2.4 MA/m (30 kOe) at 473 K and 1.6 MA/m (20 kOe) at 573 K, which shows the good temperature coefficient of coercivity of −0.22%/K. The well-organized microstructure with fine Sm-Co alloy single-crystal grains with an average grain size of 0.63 μm, sharp grain boundary, and better crystallinity, leads to a huge coercivity and remarkable thermal stability.

Mechanical properties of samarium cobalt: A molecular dynamics study

Sm-Co permanent magnets are usually very brittle which makes them vulnerable to even mild impacts. Recently, it was reported by simulation and confirmed by experiment that SmCo5 can be plastically deformed via amorphous shear bands activated by external stress. Since most Sm-Co magnets mainly consist of the Sm2Co17 phase, it is necessary to study how the Sm2Co17 phase can be deformed compared with the SmCo5 phase (existing also in Sm-Co magnets). In addition, the mechanical properties of the two-phase composites with an interface should be investigated. In this paper, we show that the Sm2Co17 phase can also be plastically deformed under tensile loading due to the formation of amorphous shear bands. We find that the interfacial stress between SmCo5 and Sm2Co17 significantly affects the formation of amorphous shear bands. The formation energies of amorphous shear bands are lower than the energies needed for transgranular, intergranular and interphase cleavage. The two-phase samples notched at the interface are also deformed by tensile loading. When the amorphous shear band is initiated in the Sm2Co17 phase, the sample quickly necks toward failure. In contrast, when amorphous shear band is initiated in the SmCo5 phase, the sample can accommodate more strain. These results help us understand the intrinsic mechanical properties of Sm-Co magnets.

Recovery of rare earths in different media with novel dicarboxylate based ionic liquid and application to recycle SmCo magnets

Recovery and separation of rare earth elements was highly crucial but difficult. In this study, a well-designed new ionic liquid named as benzyltributylammonium decanedioate ([N444Bn]2[SA]) was developed to extract rare earths and separate Sm(III) from the spent SmCo magnets in acetate medium for the first time. To exhibit the superiority of acetate medium, the extraction of Nd(III) and La(III) in three different media were comparatively investigated under different conditions, including equilibrium time, initial pH of aqueous solution, rare earth concentration, extractant concentration, salting-out agent concentration and extraction temperature. The results revealed that the better extractabilities of La(III) were observed in acetate medium rather than those in chloride medium (i.e., 97.6% versus 78.6%), which may be attributed to the low-hydrated nature of acetate ions. Importantly, the back-extraction experiments indicated that 91.4% Nd(III) can be stripped from [N444Bn]2[SA] by using 1.5 mol/L HOAc, revealing the outstanding reusability of ionic liquid in the industrial separation-stripping cycles. Furthermore, the ion association mechanism was proposed to describe the extraction behavior and confirmed by the slope analysis and FT-IR characterizations in three media. In terms of the SmCoCu mixture separation, the maximal separation factor of Sm(III)/Co(II) was calculated as 3078 in simulated solution. Impressively, the recovery of Sm(III) from the actual SmCo magnets by our dicarboxylate-type ionic liquid was also successfully achieved with a recycling rate of 96.8% and a Sm(III)/Co(II) selectivity of 148, which exhibited the potential application in the separation of Sm(III) from the spent SmCo magnets.

Mechanically strengthened heterogeneous Sm-Co sintered magnets

Samarium-cobalt sintered magnets offer excellent magnetic properties, thermal stability, and corrosion resistance. They are used in a variety of defense and civilian applications, especially when elevated operation temperatures (e.g., 200 ºC to 550 ºC) are required. However, the utilization of these materials is restricted by their brittleness. Improving their mechanical resilience would make them more cost-effective, efficient, and robust in decarbonization and other function-related applications while reducing the pressure on critical material supply chains. In this paper, we engineer a series of novel heterogeneous microstructures, such as laminated coarse grain (CG)/fine grain (FG) and core/shell CG/FG microstructures, to produce unprecedented combinations of superior mechanical and magnetic properties without altering the chemical compositions of the magnets or common heat treatment procedures. A 60% flexural strength enhancement is obtained using heterogeneous Sm2(CoFeCuZr)17 sintered magnets with little impact on their magnetic properties. The mechanically robust heterogeneous Sm-Co sintered magnets have a minor (e.g., less than 4.6%) reduction in the energy product (BH)max due to a slightly reduced squareness of the demagnetization curve, with no decrease in either the remanence (Br) or the intrinsic coercivity (Hci). The flexural strengths of these heterogeneous Sm-Co magnets depend on the volume ratios and mean grain sizes of the FG/CG regions, as well as their microstructural architectures. The fine-grained regions act as mechanical strengthening sites, which can be strategically used when designing the magnet for different applications. This technology is highly compatible with existing magnet manufacturing processes and thus can be adopted readily by the magnet industry.

Optimization of the Temperature Coefficients of Remanence and Coercivity in Sm2co17 Magnets by Dy88cu12 Doping

Optimization of the Temperature Coefficients of Remanence and Coercivity in Sm2co17 Magnets by Dy88cu12 Doping

Optimization of the Temperature Coefficients of Remanence and Coercivity in Sm2co17 Magnets by Dy88cu12 Doping

Optimization of the Temperature Coefficients of Remanence and Coercivity in Sm2co17 Magnets by Dy88cu12 Doping

Ab initio, artificial neural network predictions and experimental synthesis of mischmetal alloying in Sm-Co permanent magnets.

The use of the mischmetal alloy, comprised of La and Ce in 1 : 3 ratio, as a partial substitute for Sm in the CaCu5-type structure is explored, as a means for the search of viable alternatives for permanent magnets that require fewer steps in the rare earth separation processing. The structural and magnetic properties of the introduced stoichiometry, containing 50% less Sm, are compared to the ones of the SmCo5, LaCo5 and CeCo5 binary compounds by means of ab initio simulations. The capability of artificial neural networks to accurately predict the relationship between structure and total magnetization from DFT calculations in the supercell approach that was employed, is also demonstrated. Experimental fabrication and structural and magnetic characterization of the proposed stoichiometry verifies the structural configuration and provides insight for the macroscopic hard magnetic properties of the material. The reduction of magnetic properties was found to be favorable compared to the respective reduction of the raw materials cost, while measurements of the Cure temperature verify that the proposed compound is still suitable for high temperature applications.

Prolonged Ordering Process Induced Higher Segregation of Copper in 2:17 Type Smco Magnets

Prolonged Ordering Process Induced Higher Segregation of Copper in 2:17 Type Smco Magnets

A multiphysics model of processes in electromagnets and actuators of vacuum switching devices taking into ac-count contact interaction of structural elements

The purpose of the work is to improve mathematical models and algorithms of computer modeling of multiphysics processes in electromagnets and actuators of vacuum switching devices by taking into account the contact interaction of structural elements when changing their stress-strain state. In the design of modern vacuum circuit breakers and contactors, there is a significant use of electromagnetic actuators based on high-coercive hard magnetic rare earth composite materials NdFeB and SmCo. The most promising for use as drives of circuit breakers and contactors are polarized electromagnets based on the use of these high-coercive permanent magnets. However, the existing serial designs of electromagnets and actuators need to be significantly improved in order to increase reliability and service life, reduce weight and cost, further reduce energy consumption, improve the manufacturability of the mass production process. Computer simulation is proposed to be performed by the Finite Element Method in 2D formulation using commercial software products and/or software created directly for these investigations. One of the priority areas for improving mathematical models and algorithms for computer modeling of processes in the mechanical circuit of vacuum switching devices of medium and high voltage is to take into account the contact interaction of the structural elements of the devices under consideration. The next step, thanks to the use of an advanced mathematical model, is to perform a set of computational research and based on the obtained numerical results to develop recommendations aimed at creating designs of electromagnets and actuators that would meet world standards and be competitive in the world market.

Effect of dry thermal oxidation on the microstructure and magnetic properties of SmCo5 permanent magnet

Understanding the microstructural changes in SmCo5 because of oxidation and thereby altered magnetic properties will help in designing permanent magnets which could retain their magnetic properties in adverse environments. In this regard, the present study investigates the thermal oxidation of SmCo5 magnets by varying temperature (373−973 K), time (1, 5 h) and pressure (1.013 × 105 and 4.6 × 10−5 Pa). Increased Co segregation towards the surface is found and this impacts the overall oxidation mechanism to a large extent. In the end, the developed oxide-film microstructure and microstructural changes in the bulk are correlated with the induced changes in the magnetic properties.

Structural and magnetic properties of hard magnetic system Ce(Co1-xFex)4.4Cu0.6 (0 ≤ x ≤ 0.19)

The Ce(Co1-xFex)4.4Cu0.6 (0 ≤ x ≤ 0.19) is a composite, hard magnetic system that is based on the CaCu5-type structure (1:5). It shows both, unique magnetic and microstructural features that are essential for permanent magnets, e.g., exceptional squareness of the 2nd. quadrant of the magnetization loops and microstructural features typically needed for pinning. Samples solidified in alumina crucibles are coarse-grained and often clearly faceted and readily align in a magnetic field. X-ray, SEM, and TEM analyses show a 1:5-type single-phase material when quenched from high temperature, which, after heat treatment, transforms into a laminar coherent nanostructure through the formation of a dense array of extended intercalated regions. These extended intercalated regions are comprised of segments of the Ce2Ni7–type structure (2:7) which segregate into various closely related precipitates forming a nanostructure similar to the SmCo5 - Sm2Co17 composites seen in Sm-Co permanent magnets. Based on TEM and Lorentz microscopy of well-aligned single grain particles, the magnetic domains’ reversal mechanism is regulated by anisotropy fluctuations occurring along the easy direction of magnetization and strong exchange interactions between the matrix and defects (e.g.: stacking faults). Lorentz microscopy suggests the domain wall is not physically pinned by the defect, but rather is offset/deflected when it interacts with the defect. The Lorentz and magnetization data suggest that defects cause a bending of the moment away from the c axis inside the grains.

Anisotropic Sm-Co nanopowder prepared by induction thermal plasma

A hard magnetic Sm-Co alloy nanopowder is successfully prepared by the recently-developed low oxygen-induction thermal plasma (LO-ITP) process. Spherical particles with an average diameter of 61 nm are achieved. According to the X-ray diffraction (XRD) profile, hard magnetic compounds of SmCo5 and SmCo7 are obtained. Transmission electron microscopic (TEM) observation confirms that the Sm-Co particles have a uniaxial anisotropic structure. This work also leads to the discovery of a previously-unknown core/shell particle with a Co-core/Sm-Co-shell structure, which has an ideal interface for exchange coupling, as the particle is formed with no oxide phase in the interface between the Co-core and Sm-Co-shell. Magnetic measurements show that coercivity is 5.6 kOe at room temperature and magnetization is 80 emu/g at 9 T, and the recoil curve shows spring-back behavior, suggesting exchange-coupling between the Co-core and the Sm-Co-shell. A numerical analysis demonstrates the formation mechanism of the Sm-Co alloy particles and the core/shell particles, and also suggests a strategy for improving the magnetic properties of the Sm-Co alloy nanopowder.

Magnetic properties and resistivity of a 2:17-type SmCo magnet doped with ZrO2 * *Project supported by the National Natural Science Foundation of China (Grant No. 51877094) and Ningbo Science and Technology Project (Grant No. 2014B11009).

In order to counteract the demagnetization caused by eddy current loss, widespread attention has been devoted to increasing the resistivity of permanent magnets. We prepared 2:17-type SmCo magnets doped with different ZrO2 contents and investigated the influence of the ZrO2 content on the magnetic properties and resistive anisotropism. The results showed that not only was the resistivity of the magnet improved, but, in addition, the coercivity of the magnet was significantly increased. The microstructure was studied with TEM, which showed that ZrO2 doping was able to cause a decrease in the lamellar phase density and the growth of cellular structures. The increased grain boundaries and Sm2O3 phases were favorable to the improvement of resistivity. The decrease of the lamellar phases caused a narrowing of the resistive anisotropism. The additional Cu in the center of the cellular boundaries was the main reason for the enhancement of H cj. However, an excessive amount caused an increase of the Zr6(FeCo)23 phase and a deterioration of the cellular structure, thereby leading to a decrease in coercivity.

Electronic structure and magnetic properties of Dy-doped Bi2Te3

The electronic and magnetic character, and the magnetic anisotropy in practically important magnetic materials containing the rare earth elements are investigated making use of the correlated band theory implemented as a combination of the relativistic density functional theory with the Anderson impurity model (DFT+U+HIA). First, we demonstrate that DFT+U+HIA provides a good description of the electronic structure, spin and orbital magnetic moments, and the magnetic anisotropy for SmCo5 magnet with 4f5-like Sm3+ shell. Further, the method is applied to theoretical investigation of Dy-doped Bi2Te3 topological insulator. For both ferro- and anti-ferromagnetic Dy-planes in Bi2Te3 we found the in-gap flat f-bands located at the top of the valence band of Bi2Te3. The positive uniaxial MAE is predicted for (DyxBi1−x)2Te3 with x = 0.33. The experimental resonant photoemission spectra are well reproduced by the calculations. These studies can be important to explore the potential use of rare-earth doped topological insulators in the low-power spintronic devises.

Impact of magnetic field on the thermal properties of chemically synthesized Sm-Co nanoparticles based silicone oil nanofluid

This work aims to study the enhanced thermal conductivity of silicone oil on increasing mass % of hard magnetic Sm-Co based nanoparticles (NPs) in the presence of external magnetic fields. Sm-Co NPs were synthesized using the low temperature 'Pechini-type sol–gel' process. The presence of mixed phases is evident through XRD, FESEM, and TEM. The average hydrodynamic size of Sm-Co NPs was measured 51 nm by DLS. The study of magnetization vs. magnetic field reveals the weak ferromagnetic ordering along with the paramagnetic behaviour of the Sm-Co NPs. Thermal conductivity enhancement of Sm-Co nanofluids showed an increasing trend with the rising particle concentration and magnetic flux density. A high thermal conductivity enhancement of ~ 373% is reported at 15 mass % concentration of Sm-Co nanofluids and at a magnetic flux density of 0.5 T. The mechanism behind this thermal conductivity enhancement in the presence of an externally applied magnetic field has been discussed on the basis of near field magneto-static interactions of the magnetic nanoparticles. Microstructural, magnetic, and heat transport studies of Sm-Co based MNFs are very useful for device applications.

Rotation angle sensing system using magnetostrictive alloy Terfenol-D and permanent magnet

In this study, we developed a rotation angle sensor using the polycrystalline magnetostrictive alloy Terfenol-D, an SmCo permanent magnet, and a commercial dial gauge. The magnetostriction ΔL/L value was measured based on the variation in the electrical resistance of a strain gauge fixed on Terfenol-D. The merit of this system is that it is non-contact and can convert the measured electrical resistance directly into the angle of rotation. The ΔL/L was proportional to the distance x between Terfenol-D and the SmCo magnet. The deviation of the measured points from the fitting linear line was ±0.4%, which corresponds to ± 1.4°per 360°rotation.The developed system is suitable for rotation angle sensors. We also performed the actuation of this sensor system in variable state and compared this sensor system with giant magnetoresistance or Hall sensors; the rotational angle, maximum speed, and errors are not significantly different from those of other sensing types.

Influence of Oxygen or Carbon Impurities on Domain Structure of Sm-Co Magnets

Influence of Oxygen or Carbon Impurities on Domain Structure of Sm-Co Magnets

A cleaner strategy for comprehensive recovery of waste SmCo magnets based on deep eutectic solvents

Sustainable and comprehensive recycling of valuable elements from waste SmCo magnets is crucial. In this work, an environmentally friendly process based on low viscosity and easy preparation of hydrophobic deep eutectic solvent (HDES) for comprehensive recovery of Fe(III), Co(II), Cu(II) and Sm(III) from waste SmCo magnets has been developed. The HDESs based on dodecanol (Dodec) and tri-n-octylphosphine oxide (TOPO) were prepared, characterized and first used to selectively extract Fe(III) and Sm(III) from the SmCo magnets leachate. And then the Cu(II) and Co(II) in the raffinate were selectively separated using decanoic acid (DA):lauric acid (LA) (2:1) based HDES. The batch counter current extraction experiment was carried out under optimal conditions. After two-stage extraction by using Dodec:TOPO (2:1) based HDES, over 99% of the Fe(III) and Sm(III) were extracted into the organic phase. Subsequently, the raffinate containing Co(II) and Cu(II) was subjected to single-stage extraction and three-stage scrubbing using DA:LA (2:1) based HDES. Fe(III) and Sm(III) loaded in the Dodec:TOPO (2:1) based HDES phase could be stripped by using 1.5 mol/L H2C2O4. The obtained Fe2(C2O4)3 solution and Sm2(C2O4)3 precipitate were separated by filtration. And the Cu(II) loaded in the DA:LA (2:1) based HDES phase was stripped by using 1 mol/L H2SO4. Finally, Fe(III), Co(II), Cu(II) and Sm(III) were completely separated, and the purity of each product can reach 98.50% or higher. The recovery rates of Fe(III), Co(II), Cu(II) and Sm(III) were 99%, 99%, 96.47% and 99%, respectively. The process has lower chemical consumption and no need to use volatile and toxic organic solvent, which is conducive to cleaner and safer production.

Chromatographic separation of rare earths from aqueous and ethanolic leachates of NdFeB and SmCo magnets by a supported ionic liquid phase.

The separation of rare-earth elements (REEs) from other components of end-of-life NdFeB and SmCo magnets was investigated by column chromatography. A carboxylic-acid functionalized supported ionic liquid phase (SILP) was studied as a stationary phase. The magnets were firstly leached with a dilute aqueous or ethanolic hydrochloric acid solution at room temperature. Leaching of REEs from a NdFeB magnet was similarly efficient with both lixiviants, but the REEs were more efficiently leached from a SmCo magnet with the ethanolic lixiviant. The SILP exhibited a high affinity towards trivalent cations of REEs, which were successfully recovered from the aqueous and ethanolic leachates of magnets. Divalent cations of iron and cobalt, which were the major components of the acidic aqueous leachates of magnets, were rejected by the SILP. Iron and cobalt were present as negatively charged chloro complexes in the ethanolic leachates of magnets, and were not recovered by the cation-exchanging SILP. A versatile column chromatography method is developed, suitable for the separation of REEs from iron and cobalt, either from aqueous or ethanolic leachates of permanent magnets.

Techno-economic Assessment of a Novel SmCo Permanent Magnet Manufacturing Method

Rare earth elements (REEs) are becoming ever more important and broadly used in rare earth permanent magnets (REPMs) for electric vehicles, wind turbines, cell phones, etc. While neodymium-iron-boron (NdFeB) magnets are very popular, samarium cobalt (SmCo) magnets are increasingly being viewed as an alternative REPM option due their better resistance to corrosion and oxidation. These properties position SmCo for wide use in high temperature and extreme working environments. As is well known, the availability of REEs for many applications is subject to substantial risk owing to the dependence on China for REE containing ores and processing. Though recycling end-of-life (EOL) magnets would help alleviate the supply chain crisis, lowering the failure rate during manufacturing will more effectively utilize the resources that are available. Techno-economic assessments (TEAs) were performed for a traditional and a novel process to manufacture SmCo magnets. The results show that the novel process is economically feasible and more resistant to the vagaries of market price changes.