Permanent Magnet Applications Research Articles

Extraction and recovery of rare earth elements from NdFeB waste using bismuth reinforced by supergravity

NdFeB stands as the foremost utilized material in permanent magnet applications, generating substantial quantities of NdFeB magnet waste annually. These wastes contain 20−30 wt. % rare earth elements (REEs) and are valuable secondary resources. In this paper, Bi was used as extractant to recover REEs in NdFeB waste by pyrometallurgy, and excess Bi was separated by supergravity technology for recycling. The migration and diffusion behaviors of REEs during the extraction process were investigated, with the diffusion coefficient of REEs in Bi obtained. The influence of Bi-to-waste mass ratio on rare earth extraction efficiency in smelting process, alongside the effect of temperature and gravity coefficient on the Bi recovery rate in supergravity centrifugation process were delineated. Findings revealed that the diffusion of Nd in Bi and NdFeB conformed to Fick's second law. Notably, with a Bi-to-waste mass ratio surpassing 1:1, spontaneous separation occurred between the Bi and Fe phases, facilitating the migration of almost all REEs from NdFeB waste into the Bi phase. Under the optimal conditions (Bi/NdFeB mass ratio of 4:3, separation temperature of 500°C and a gravity coefficient of 1000), the recovery rate of REEs during the smelting stage reached 99.6%, while the Bi recovery rate during the supergravity stage was 74.7%. Additionally, the overall REE recovery rate and Bi recovery rate during the entire process reached 99.3% and 70.3%, respectively. The successful development of this process has opened up a new way for recycling REEs from NdFeB waste.

Machine learning assisted search for Fe–Co–C ternary compounds with high magnetic anisotropy

We employ a machine learning (ML)-guided framework to explore rare earth free magnetic materials, specifically focusing on Fe–Co–C ternary compounds for potential use in permanent magnets. Utilizing a specifically trained crystal graph convolutional neural network model, we efficiently screen a vast space of nearly a million substitutional structures to select 620 promising structures for further investigation by first-principles calculation. We predict five low-energy metastable Fe–Co–C compounds with formation energy less than 150 meV/atom above the convex hull. These compounds exhibit high magnetization (Js > 1.0 T) and significant magnetic anisotropy (K1 > 1.0 MJ/m3), making them promising candidates for permanent magnet applications. The phonon calculations indicate these compounds are dynamically stable. Our ML-guided framework demonstrates the utility of rapidly identifying novel materials with tailored magnetic properties.

Optimizing the composition of (Ce,La)(Co,Fe)5for permanent magnet applications using density functional theory.

In this work, we calculated physical quantities, including the magnetocrystalline anisotropy constant (Ku) and magnetization (Ms), for disordered (Ce,La)(Co,Fe)5systems. Based on the results, we propose CeCo4.7Fe0.3as the optimum composition for high-performance permanent magnets. The calculations employed the full-potential Korringa-Kohn-Rostoker Green's function method, and dealt with the compositional disorder of the systems within the coherent potential approximation. It was found that the La doping reducesKuat 0 K but increases the Curie temperature (TC), which leads to improvement of the magnetic properties at high temperatures. CeCo4.7Fe0.3had the largest magnetic anisotropy ofKu= 15.14 MJ/m3, which is larger than that of CeCo5(Ku= 14.77 MJ/m3).TCof CeCo4.7Fe0.3estimated by the mean-field approximation was 1005 K, which exceeds that of CeCo5(965 K). Further, our calculations showed that while doping of Fe destabilizes the system, CeCo4.7Fe0.3is stable against decomposition into the simple substances. We also show calculated data that are informative for exploring high-performance permanent magnet materials in this paper.

Exploring the effect of exchange coupling in (SrFe9.8Al2La0.2O19)1-x/(Co0.7Zn0.3Fe2O4)x nanocomposites synthesised by sol–gel auto combustion method

Extensive research has been conducted over the last decade to develop permanent magnets utilizing less rare earth materials. Exchange-coupled nanocomposite magnets are a fascinating development in the field of permanent magnets. They involve the combination of hard and soft ferrites, resulting in a unique and evolving magnet. Here we present an in-depth structural, morphological and magnetic characterization of ferrite-based nanostructures obtained through a bottom-up sol−gel approach. The combination of high coercivity of a hard phase SrFe9.8Al2La0.2O19 (SFALO) and high saturation magnetization of a soft phase, Co0.7Zn0.3Fe2O4 (CZFO), allowed us to develop exchange-coupled bi-magnetic nanocomposites by varying the mass percentage (x = 0, 0.1, 0.2, 0.3, 0.4, 1). Thermogravimetric analysis (TGA) up to 1200 °C was used to investigate the material’s thermal properties with the phase formation temperature. Detailed atomic/nano-scale structural characterizations of these nanocomposites were performed by X-ray diffraction and Transmission Electron Microscopy. The average particle size was calculated from the SEM analysis and it was observed that most of the composites with ratio x = 0.1, 0.3 & 0.4 was 145 nm and x = 0.2 was 165 nm. The Switching Field Distribution (SFD) curve revealed the exchange coupling between soft and hard magnetic particles. The findings indicate that the inclusion of a soft magnetic phase has a considerable impact on the exchange coupling between the hard and soft ferrite phases. As the spinel concentration increased, in the composite the saturation magnetization increased from 18 emu/g to 48 emu/g. From the stroner-wholfrathmodel, the decrease in the remanence ratio below 0.5 concludes the crystallites are randomly oriented. The nanocomposite with the ratio x = 0.1 was observed with the high magneto crystalline anisotropy of 2183.23 × 102 (J/m3) and a high energy product (BH)max of 5.5 kJ/m3. The aforementioned features of nanocomposites demonstrate their potential for use in permanent magnet applications.

Transformation of in-plane to out-of-plane anisotropy in MnBi alloy for permanent magnet application: a First-principles study

The low-temperature phase (LTP) MnBi exhibits remarkable ferromagnetic properties at room temperature. However, below its Curie temperature (TC\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${T}_{C}$$\\end{document}), a phase transition occurs around 613 K due to diffusion of Mn into interstitial sites, raising concerns about its structural and magnetic properties. Furthermore, the presence of in-plane anisotropy in LTP-MnBi alloy at low temperatures raises concerns about its suitability for use in permanent magnet applications, even at higher temperature. Therefore, this study examines the structural and magnetic properties of pure LTP-MnBi and its successive Ni-doped and Fe-substituted alloys using first-principles study based on density functional theory (DFT). To prevent Mn diffusion into interstitial sites, Ni doping is employed. Additionally, the incorporation of Ni successfully addresses the in-plane anisotropy issue in LTP-MnBi, transforming it into out-of-plane anisotropy. Moreover, we explored the potential advantages of substituting Fe for one of Mn site. This substitution aims to improve the observed dynamical instability in Ni-doped alloy and to further enhanced the magnetocrystalline anisotropy energy (MAE) of the material, resulting in an MAE of 3.21 MJ/m3, along with a TC\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${T}_{C}$$\\end{document} of 523 K. Therefore, the coexistence of high MAE and moderate TC\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${T}_{C}$$\\end{document} in the Mn0.5Fe0.5Bi–Ni alloy presents viable option for its application in permanent magnet technology.

Study on the structural, magnetic, and magnetodielectric properties of M-type BaFe12O19 and SrFe12O19 hexaferrite nanoparticles

This study addresses the synthesis and characterization of hexagonal barium hexaferrite (BaFe12O19) and strontium hexaferrite (SrFe12O19) nanoparticles, aiming to enhance their structural and magnetic properties for potential applications. Using the sol–gel method, nanoparticles were synthesized and calcinated at 1000 °C, 1100 °C, and 1200 °C for 5 h. A comprehensive analysis was conducted on the prepared nanoparticles' structural, functional, morphological, and magnetic properties. X-ray diffraction confirmed the hexagonal structure and single-crystal phase for BaFe12O19 and SrFe12O19 across all calcination temperatures. The Rietveld analysis of XRD patterns of all the samples have been carried. Fourier transform infrared spectroscopy identified fundamental vibrations at octahedral and tetrahedral sites, verifying the presence of characteristic functional groups. Morphological studies revealed that at an annealing temperature of 1100 °C, the average nanoparticle diameters were 335 nm for BaFe12O19 and 302 nm for SrFe12O19. The elemental analysis and distribution of elements of hexaferrites were studies using Energy Dispersive X-ray Analysis with color mapping method. Magnetic properties were extensively analyzed, including saturation magnetization (Ms), coercivity (Hc), retentivity (Mr), anisotropy field (Ha), squareness ratio (Mr/Ms), and magnetocrystalline anisotropy (K1). At 1100 °C, the magnetic properties of BaFe12O19 are Ms = 55.96 emu/g, Hc = 4308 G, Mr/Ms = 0.51, Ha = 31.30 kG, and K1 = 5.65 × 105 erg/cm3. For SrFe12O19, these values are Ms = 50.80 emu/g, Hc = 3507 G, Mr/Ms = 0.52, Ha = 21.20 kG, and K1 = 5.65 × 105 erg/cm3. Additionally, the study explored the magnetodielectric properties of BaFe12O19 and SrFe12O19 nanoparticles. At a magnetic field of 6000 G, the magnetocapacitance percentage (MC%) and magnetotangent loss percentage (ML%) for BaFe12O19 are −6.23 % and −8.85 %, respectively, while for SrFe12O19, these values are −4.38 % and −1.0 %. The findings indicate that the synthesized hexaferrite BaFe12O19 and SrFe12O19 nanoparticles exhibit significant potential for applications in sensors, permanent magnets, and data recording, with optimized structural and magnetic properties achieved at specific calcination temperatures.

Microstructure and coupling mechanisms in MnBi–FeSiB nanocomposites obtained by spark plasma sintering

Fabrication and extensive characterization of hard-soft nanocomposites composed of hard magnetic low-temperature phase LTP-MnBi and amorphous Fe70Si10B20 soft magnetic phase for bulk magnets are reported. Samples with compositions Mn55Bi45 + x⋅(Fe70Si10B20) (x = 0, 3, 5, 10, 20 wt.%) were prepared by spark plasma sintering of powder mixtures. Characterization has been performed by X-ray diffraction, scanning and transmission electron microscopy, magnetometry and 57Fe Mӧssbauer spectroscopy. It was shown that samples contain crystallized and nanometric LTP-MnBi phases with various elemental compositions depending on the degree of Bi clustering. Complex correlations between starting compositions, processes during fabrication, and functional magnetic characteristics were observed. Unexpected special situations of the relation between microstructure and magnetic coupling mechanisms are discovered. Exchange spring effects of different strengths occur, being very sensitive to morpho-structural and compositional features, which in turn are controlled by processing conditions. An in-depth analysis of related microscopic characteristics is provided. Results of this work suggest that fabrication by powder metallurgy routes, such as spark plasma sintering of hard and soft magnetic powder mixtures, of MnBi-based composites with exchange spring phenomena have a high potential in designing and optimization of suitable materials with tunable magnetic properties towards rare-earth–free permanent magnet applications.

Investigation of a novel intensifying-flux hybrid excited permanent magnet machine for electric vehicles

PurposeTo address the issues of the insufficient output torque associated with the application of intensifying-flux permanent magnet (PM) machines in electric vehicles, this paper aims to propose an intensifying-flux hybrid excitation PM machine. It is possible to adjust the air gap magnetic field by adjusting the field current in the excitation winding, thereby increasing the torque output capability and speed range of the machine.Design/methodology/approachFirst, a novel intensifying-flux hybrid excited permanent magnet synchronous machine (IF-HEPMSM) is proposed on the basis of intensifying-flux permanent magnet synchronous machine (IF-PMSM) and an equivalent magnetic circuit model is established. Second, the tooth width and yoke thickness of the machine stator are optimized to ensure the overload capacity of the machine while effectively improving the wide flux regulation range. Furthermore, the electromagnetic characteristics of the IF-HEPMSM are investigated and compared with the IF-PMSM and conventional permanent magnet synchronous machine (PMSM) by using finite element simulations.FindingsThe id of IF-HEPMSM and IF-PMSM is greater than zero low-speed magnetizing current. And the flux-weakening current of the IF-HEPMSM is 18% and 3% smaller than of the conventional PMSM and IF-PMSM.Practical implicationsAiming at the problems of IF-PMSM applied to electric vehicles, this paper proposes an IF-HEPMSM. The air gap magnetic field is adjusted by controlling the current of the excitation winding to improve the reliability of the machine. Therefore, the IF-HEPMSM combines the advantages of high-power density and high efficiency of the PMSM and the controllable magnetic field of the electro-excitation machine, which is of great engineering value when applied in the field of electric vehicles.Originality/valueThe proposed IF-HEPMSM offers better flux regulation capability with electromagnetic characteristics analysis and maps of dq-axis current as compared to IF-PMSM and conventional PMSM. Moreover, the improvement of the torque can make up for the shortcomings of the insufficient torque output capability of the IF-PMSM.

Al3Sc phase uniform distribution and aluminum grains refinement in Al-2Sc alloy achieved by NdFeB permanent magnet stirring

The rapid development of magnetic materials provides the possibility for the application of permanent magnet stirring (PMS). Numerical and experimental investigations were employed with respect to the solidification process of the Al-2Sc alloy controlled by a novel PMS using NdFeB permanent magnets under various rotation speeds (0, 50, 100 and 150 r/min). The simulated results reveal that the maximum electromagnetic force increases proportionally from 4.14 to 12.39 kN/m3 and the maximum tangential velocity increases from 0.13 to 0.36 m/s when the rotation speed of PMS enhances from 50 to 150 r/min in the ingot melt. Besides, the experimental results demonstrate that PMS can achieve a uniform distribution of blocky Al3Sc precipitated phase in the longitudinal direction under the impact of a forced fluid flow. Moreover, increasing rotation speed of PMS is beneficial to refining aluminum grain size significantly and decreasing the texture intensity in the alloy. In addition, the Brinell hardness of Al-2Sc alloy is increased by 33% to 27.8 HB and the tensile strength is enhanced by 34% to 128.2 MPa, due to the improved distribution of the strengthening Al3Sc phase and the grain refinement of Al matrix under the impact of PMS. This work provides an effective application of NdFeB permanent magnets in the metal cast field.

Optimizing the Sintering Conditions of (Fe,Co)1.95(P,Si) Compounds for Permanent Magnet Applications.

(Fe,Co)2(P,Si) quaternary compounds combine large uniaxial magnetocrystalline anisotropy, significant saturation magnetization and tunable Curie temperature, making them attractive for permanent magnet applications. Single crystals or conventionally prepared bulk polycrystalline (Fe,Co)2(P,Si) samples do not, however, show a significant coercivity. Here, after a ball-milling stage of elemental precursors, we optimize the sintering temperature and duration during the solid-state synthesis of bulk Fe1.85Co0.1P0.8Si0.2 compounds so as to obtain coercivity in bulk samples. We pay special attention to shortening the heat treatment in order to limit grain growth. Powder X-ray diffraction experiments demonstrate that a sintering of a few minutes is sufficient to form the desired Fe2P-type hexagonal structure with limited secondary-phase content (~5 wt.%). Coercivity is achieved in bulk Fe1.85Co0.1P0.8Si0.2 quaternary compounds by shortening the heat treatment. Surprisingly, the largest coercivities are observed in the samples presenting large amounts of secondary-phase content (>5 wt.%). In addition to the shape of the virgin magnetization curve, this may indicate a dominant wall-pining coercivity mechanism. Despite a tenfold improvement of the coercive fields for bulk samples, the achieved performances remain modest (HC ≈ 0.6 kOe at room temperature). These results nonetheless establish a benchmark for future developments of (Fe,Co)2(P,Si) compounds as permanent magnets.

The effects of V doping on the intrinsic properties of SmFe10Co2 alloys: A theoretical investigation

The present study focuses on the intrinsic properties of the SmFe10Co2-xVx (x = 0–2) alloys, which includes the SmFe10Co2 alloy, one of the most promising permanent magnets with the ThMn12 type of structure due to its large saturation magnetization (µ0Ms = 1.78 T), high Curie temperature (Tc = 859 K), and anisotropy field (µ0Ha = 12 T) experimentally obtained. Unfortunately, its low coercivity (<0.4 T) hinders its use in permanent magnet applications. The effect of V-doping on magnetization, magnetocrystalline anisotropy energy, and Curie temperature is investigated by electronic band structure calculations. The spin-polarized fully relativistic Korringa-Kohn-Rostoker (SPR-KKR) band structure method, which employs the coherent potential approximation (CPA) to deal with substitutional disorder, has been used. The Hubbard-U correction to local spin density approximation (LSDA + U) was used to account for the large correlation effects due to the 4f electronic states of Sm. The computed magnetic moments and magnetocrystalline anisotropy energies were compared with existing experimental data to validate the theoretical approach’s reliability. The exchange-coupling parameters from the Heisenberg model were used for obtaining the mean-field estimated Curie temperature. The magnetic anisotropy energy was separated into contributions from transition metals and Sm, and its relationships with the local environment, interatomic distances, and valence electron delocalization were analyzed. The suitability of the hypothetical SmFe10CoV alloy for permanent magnet manufacture was assessed using the calculated anisotropy field, magnetic hardness, and intrinsic magnetic properties.

Structural and magnetic properties of M-type hexaferrite nanoparticles: A comparative analysis of BaFe12O19 and SrFe12O19 synthesized via chemical co-precipitation

In this work, a comprehensive analysis of the structural and magnetic properties of the M-type hexaferrite (BaFe12O19 and SrFe12O19) was conducted using the chemical co-precipitation approach. The analytical techniques employed include powder X-ray diffraction, Transmission Electron Microscopy, Fourier Transform Infrared Spectroscopy, and Thermogravimetric Analysis. Powder Neutron Diffraction was utilized to analyse the magnetic ordering and crystal structure. A hexagonal crystal structure with space group P63/mmc was obtained from to structural analysis. Additionally, the investigation encompassed an assessment of the maximum energy product (BH)max and magnetic properties utilizing Vibrating Sample Magnetometry across all synthesized materials. Magnetic investigations of the studied materials showed several interesting characteristics: SrM showed a maximum saturation magnetization of 49.67 emu/g and a maximum coercivity of 4874.55 Oe. Remarkably, SrFe12O19 showed twice as much saturation magnetization and remnant magnetization than BaFe12O19, suggesting more robust and effective magnetic parameters. The overarching objective of this study is to discern the optimal hexaferrite material, evaluating magnetism, coercivity, thermal stability, and energy output through a systematic exploration of crystal structure, magnetic properties, thermal behaviour, manufacturing methodologies, and microstructure. This research endeavour not only contributes crucial insights into the potential applications of both BaM and SrM but also considers their environmental implications. The study further provides valuable recommendations for selecting the most efficacious material for specific permanent magnet applications, thereby contributing to the advancement on the field of magnetic engineering. The culmination of this work is poised to facilitate informed decision-making and technological progress in the realm of hexaferrite materials with a deliberate consideration of their environmental impact.

Vector hysteresis loops of rare earth magnets measured in a biaxial vibrating sample magnetometer

Vector hysteresis loops of rare earth magnets measured in a biaxial vibrating sample magnetometer

Tuning the magnetic properties of hard–soft Ba0.5Sr0.5Fe10Al2O19 and Ni0.1Co0.9Fe2O4 nanocomposites via one pot sol–gel auto combustion method for permanent magnet applications

Permanent magnets generate magnetic fields that can be sustained when a reverse field is supplied. These permanent magnets are effective in a wide range of applications. However, strategic rare-earth element demand has increased interest in replacing them with huge energy product (BH)max. Exchange-coupled hard/soft ferrite nanocomposites have the potential to replace a portion of extravagant rare earth element-based magnets. In the present, we have reported the facile auto combustion synthesis of exchange-coupled Ba0.5Sr0.5Fe10Al2O19 and Ni0.1Co0.9Fe2O4 nanocomposites by increasing the content of soft ferrite over the hard from x = 0.1 to 0.4 wt%. The XRD combined with Rietveld analysis reflected the presence of hexaferrite and spinel ferrite without the existence of secondary phases. The absorption bands from the Fourier transform infrared spectrum analysis proved the presence of M–O bonds in tetrahedral sites and octahedral sites. Rod and non-spherical images from TEM represent the hexaferrite and spinel ferrite. The smooth M–H curve and a single peak of the switching field distribution curve prove that the material has undergone a good exchange coupling. The nanopowders displayed an increase in saturation magnetization and a decrease in coercivity with the increases in the spinel content. The prepared nanocomposites were showing higher energy products. The composite with the ratio x = 0.2 displayed a higher value of (BH)max of 13.16 kJ m−3.

Effect of Ni and Ni/Cr Coating on Corrosion and Magnetic Behavior of Sm2Co17 Substrate for Permanent Magnet Application in Marine Environment

Effect of Ni and Ni/Cr Coating on Corrosion and Magnetic Behavior of Sm2Co17 Substrate for Permanent Magnet Application in Marine Environment

Investigation on the structure-optimized magnetic properties of hydrothermally synthesized SrBi2−X(CF)XNb2O9 multiferroic nanocomposites

Hydrothermally synthesized nano multiferroic SrBi2-X(CF)XNb2O9 (SBN-CF), (CF = CoFe2O4 & X = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5) composite’s structure correlated magnetic attributes in view of reaction, exchange, and transport of ions have been comprehended from the perspective of electronic sector applications. The produced materials’ phase genesis, morphology, chemical composition, and magnetic characteristics were studied by XRD/Rietveld analysis, FEGSEM/EDS, FTIR, and VSM respectively. The Rietveld analysis of XRD data confirmed a single-phase orthorhombic structure of SBN. Further ferroelectric and cubic spinel structures of the ferrite phase have been noticed from the introduction of CF into the SBN host matrix. The crystallite size as computed (∼23–41 nm) from Debye Scherer’s formula was found to increase with dopant concentration. The imbibed morphological changes necessitated octahedral-shaped grains. The stoichiometric proportion with pronounced absorption bands is evident in EDS and FTIR studies. The impact of CF on SBN was unraveled at room temperature from the VSM study. The saturation magnetization was increased from 0.00 to 3.96 emu g−1, and the obtained coercivity values enhanced from 0.50 to 1400 Oe, due to the random fluctuations of the energy due to domain wall movements, interacting with the defective structure of the SBN material. The stress-induced distortion due to the variation in concentration of CF in SBN was configured from Y-K angles and increased from 33.55° to 61.49°. The high coercivity with a squareness value of less than 0.5 enunciates the genesis of a new class of materials for use in permanent magnet applications and memory devices.

Optimization of Ca–Al–Mn–Si Substitution Level for Enhanced Magnetic Properties of M-Type Sr-Hexaferrites for Permanent Magnet Application

Enhanced hard magnetic properties were achieved in M-type hexaferrite by optimizing the substitution levels of Mn, Al, and Si for Fe, and Ca for Sr within SrFe12O19. The addition of Al–Si–Mn effectively controlled crystallite growth, resulting in an increased coercivity (HC), while causing a decrease in the remanent magnetization (4πMr). A higher Ca content exhibited a trend of increasing the sintered density but decreasing the 4πMr and HC. The optimized composition, considering both the 4πMr and HC, was determined to be Sr0.8Ca0.2Fe10.2Mn0.1Al0.2Si0.1O19−d, with a sintered density of 4.84 g/cm3, 4πMr = 2.22 kG, and HC = 5.10 kOe. This result demonstrates the achievement of isotropic magnets with controlled crystal growth and densification without additional sintering additives. This development is promising, as this enhancement could be achieved without the use of cobalt, an expensive but essential ingredient in high-performance permanent magnets.

Enhancing structural and magnetic properties of BaFe12O19 nanoparticles through co-substitution (Co-Mn): A promising approach for permanent magnet applications

In-depth study into the creation and improvement of rare-earth free permanent magnets, particularly ferrites, has been sparked by recent economic and environmental concerns. M-type barium hexaferrites (BaFe12O19, pure BHF) are a class of low-cost permanent magnets with an excellent curie temperature and good resistance to oxidation and corrosion that are significant from a technological perspective. In the current study, the experimental conditions are optimized to obtain barium hexaferrite (BaFe12O19) co-substituted with transition elements (Co and Mn) (BaFe12–2xCoxMnxO19) via the chemical co-precipitation method. In this framework, different substitution possibilities will be investigated. The structure, morphology, vibrational spectrum, and thermal stability of the generated nanoparticles were revealed using powder x-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Rietveld refinement was used to estimate the average bond length and bond angle in order to determine the impact of superexchange interaction. Based on more precise structural characteristics, the atomic occupation and distribution of bonds are depicted from their charge density graph. For all the synthesized materials, the maximum energy product (BH)max and magnetic characteristics (VSM) were also investigated. The potential causes of this phenomenon were examined and discussed at length.

First-principles study on the enhancement of structure stability and magnetocrystalline anisotropy energy of L10-ordered Mn1−xFexAlC compound for permanent magnet application

L10-MnAl exhibits excellent magnetic properties and could be used as a candidate to fill the gap between hard ferrite and rare-earth based permanent magnet (PM) applications. However, one of the major problems with L10-MnAl is that the structure is metastable and decomposes to other structural phases at higher temperature. Therefore, enhancing the structure stability of L10-MnAl is essential for PM applications. We studied the prospect of improving the structural stability and increasing the uniaxial magnetic anisotropy energy (Ku) of the L10-MnAl structure in this work. It is found that C-doping at the 1d interstitial site enhanced the structure stability of the compound. Moreover, Fe substitution on Mn sites shows a significant increase in the uniaxial magnetic anisotropy energy (Ku). Therefore, the electronic structure and magnetic properties of L10-ordered Mn1−xFexAlC (x = 0, 0.125, 0.250, 0.375, 0.50, 0.625, 0.75, and 0.87) alloys are investigated by using the first-principles calculations. The results show that x = 0.375 Fe content in the L10-MnAl alloy and 6% doping of C maintained the structural stability and provided a maximum value of Ku = 2.13 (MJ/m3), which is 25% higher than for the pristine L10-MnAl, making it suitable for permanent magnet applications.

Magnetocrystalline anisotropy of interstitially and substitutionally Sn-doped MnBi for high temperature permanent magnet applications

First-principles calculations were performed to calculate the electronic structures of low temperature phase (LTP) MnBi (Mn50Bi50) and substitutionally and interstitially Sn-doped MnBi [Mn50Bi25Sn25, (Mn0.5Bi0.5)66.7Sn33.3]. Brillouin function predicts the temperature dependence of saturation magnetization M(T). Sn substitution for Bi in MnBi (Mn50Bi25Sn25) changes the magnetocrystalline anisotropy constant (Ku) from −0.202 MJ/m3 (the in-plane magnetization) for LTP MnBi to 1.711 MJ/m3 (the out-of-plane magnetization). In comparison, the Ku remains negative but slightly decreases to −0.043 MJ/m3 when Sn is interstitially doped in MnBi [(Mn0.5Bi0.5)66.7Sn33.3]. The Curie temperature (TC) decreases from 716 K for LTP Mn50Bi50 to 445 K for Mn50Bi25Sn25 and 285 K for (Mn0.5Bi0.5)66.7Sn33.3. Mn50Bi25Sn25 has a lower magnetic moment of 5.034 μB/f.u. but a higher saturation magnetization of 64.2 emu/g than (Mn0.5Bi0.5)66.7Sn33.3 with a magnetic moment of 6.609 μB/f.u. and a saturation magnetization of 48.2 emu/g because the weight and volume of the substitutionally Sn-doped MnBi are smaller than the interstitially Sn-doped MnBi. The low Curie temperature and magnetization for Sn-doped MnBi are attributed to the high concentration of Sn. Thus, future study needs to focus on low Sn-concentrated MnBi.