Coercivity Mechanism Research Articles

Cu-doped nanocomposite Pr2Fe14B/α-Fe ribbons with high (BH)max

Abstract The melt-spun ribbons of nominal composition Pr9Fe84.2-xB6.2P0.3Zr0.3Cux (x=0, 0.5, 1, 2) were prepared at wheel speeds of 21, 27, 30, and 33 ms-1. The XRD patterns show that as the wheel speed increases, the crystallinity of the 2:14:1 hard phase decreases, while that of the α-Fe soft phase increases. The (BH)max, remanence, and coercivity are improved from 63 kJm-3, 0.85 T, and 515 kAm-1 for the Cu-free ribbons to 171 kJm-3, 1.08 T, and 684 kAm-1 with x=0.5. The high squareness ratio of Jr/Js ~ 0.82 at 0.5 at. % Cu (27 ms-1) indicates strong exchange coupling due to small grain sizes of 15 and 30 nm for soft and hard magnetic phases, respectively. The SEM images revealed smooth morphology and uniform element distribution at 0.5 at. % Cu (27 ms-1), contributing to the high magnetic properties. The low recoil permeability (μ rec ) value of 5.466×10-4 to 1.970×10-4 $\frac{T}{k A m^{-1}}$ confirms the strong exchange coupling with x=0.5 (27 ms-1). The initial magnetization curves show that the coercivity mechanism of the Cu-free alloy evolves from the nucleation of the reverse domain to the domain wall pinning as the wheel speed increases, resulting in a high coercivity value of 818 kAm-1 (33 ms-1). Conversely, for the Cuadded alloy, the coercivity mechanism changes from pinning to the nucleation of the reverse domain from low to high wheel speed.

Challenges in implementing COP 21 obligations in Brazil until 2022

The article examines the challenges Brazil faced in implementing its obligations under the Paris Agreement (COP 21) up to 2022, focusing on the agricultural, energy, and transportation sectors, while also addressing the political obstacles that complicated the process. The study highlights the need for an integrated and coordinated approach, emphasizing the importance of public policies aimed at promoting clean energy, sustainable transportation, and more environmentally friendly agricultural practices. The Brazilian case reveals specific difficulties, including deforestation in the Amazon, the scarcity of financial resources, and economic pressures that often prioritize economic growth over environmental concerns. The article also explores the complexities of Brazil's political and economic context, discussing the challenges of balancing economic development with environmental sustainability. Despite the ambitious goals set by the Paris Agreement, the lack of coercive mechanisms and internal political divergences represent significant barriers to the effective implementation of environmental measures in the country, requiring greater commitment and coordination between public and private sectors.

Lamellar Zr-rich phase and its influence on coercivity for Sm(CoFeCuZr)z magnets

The precipitation-hardened Sm-Co permanent magnets relied on the pinning of nanocellular structures to achieve high coercivity, and have an irreplaceable position in high-temperature applications. In this article, by employing micromagnetic simulations and magnetic domain observations, the pinning behavior of lamellar phases (Z-phase) were investigated, which has not been well understood before. The results showed that the Z-phase can serve as a strong pinning position, but due to the parallel lamellar distribution, the magnetic domain walls can move around. Additionally, the effect of Z-phase on coercivity was achieved by changing the morphology of magnetic domain walls during magnetization reversal. For attractive pinning, the coercivity was reduced by the Z-phase, while for repulsive pinning, the Z-phase increased the coercivity when γZ＜0.54γH. Our findings can provide a novel understanding of the coercivity mechanism of precipitation-hardened Sm-Co permanent magnets.

Coercivity mechanism and magnetization reversal of anisotropic La-Nd-Dy-Fe-B micron-sized films

The coercivity mechanism and magnetization reversal process of anisotropic La-Nd-Dy-Fe-B micron-sized films have been investigated. By varying the thickness of the single-layer film from 500 nm to 6 μm, the highest coercivity of 1.88 T in the film with 3 μm thickness is achieved at 300 K, due to the large dipole interaction and domain pinning effect. When the thickness is further increased to 6um, the coercivity decreases sharply to 1.11T due to the microstructure and phase formation in the film. In the 6 μm multilayer film, the addition of a Ta spacer layer further enhances perpendicular magnetic anisotropy, the dipole interaction, and adjusts the phase distribution, collectively boosting the coercivity of the micron-sized film (1.63 T). As thickness of the film increases, the dominant mechanism of coercivity shifts from a pinning mechanism to a nucleation mechanism. This study contributes to the understanding of the coercivity mechanism and magnetization reversal process in La-Nd-Dy-Fe-B permanent magnet micron-sized films.

Achieving high-performance regeneration of grain boundary diffusion Nd-Fe-B sludge via an ultra-short process

The grinding sludge of grain boundary diffusion Nd-Fe-B magnet is rich in heavy rare earth and has a typical core–shell microstructure. In this work, an ultra-short process was developed to realize green, in-situ regeneration of the sludge and efficient reuse of heavy rare earth elements. The regenerated magnets showed excellent magnetic performance and good temperature stability which were fabricated after the purification of sludge, composition regulation with rare earth-rich compounds, Nd42.1FebalB0.79, NdHx, (PrNd)Hx, and sintering. Especially, the magnet prepared by using Nd42.1FebalB0.79 alloy had significant property recovery, where remanence and coercivity were restored to 12.8 kG, and 20.6 kOe, respectively, reaching 97.7 % and 162.5 % of the original magnet. The magnetization reversal behavior and the coercivity mechanism were analyzed to keep the nucleation mechanism, and the high coercivity stemmed from the repair and optimization of the grain boundary by introducing rare earth-rich alloys, the full utilization of heavy rare earth elements, and the core–shell microstructure rooted in the sludge as well.

Phase structure evolution and coercivity mechanism of high-Co containing permanent magnets

Abstract The phase structure and magnetic properties of high-Co containing permanent magnets with high thermal stability have been systematically studied in this work. It is abnormal that the coercivity of annealed samples is slightly lower than that of sintered samples, while the coercivity was usually enhanced after annealing in conventional Nd-Fe-B samples. Further analysis showed that in addition to RE2(Fe,Co)14B main phase and RE-rich grain boundary phase, there are also new Co-rich magnetic phase located in the grain boundary. During annealing, the phase structure of high-Co containing magnets were readjusted, especially the increasing Co-rich magnetic phase and emerging RE-rich particles precipitated from the main phase. Eventually, the isolated RE-rich particles would act as the pinning center of the domain wall movement in demagnetization process. It was confirmed that the coercivity of annealed high-Co containing magnets was controlled by both nucleation and pinning. Pinning mechanism can partially compensate for the weakening of magnetic isolation due to increased Co-rich magnetic phase, which explained the moderate decrease in coercivity of annealed high-Co containing magnets. The discovery of new coercivity mechanism contributed to in-depth understanding of high-Co containing magnets.

Hydro Political Relation in the Eastern Nile Basin

Abstract Hydropolitical relations have long attracted the world of academia, and hydrohegemony and counter-hydrohegemony frameworks have recently become important in analysing power relations between riparian states. However, little attention has been given to the hydrohegemonic situation of the Nile River. This study tries to analyse this status, specifically in the Eastern Nile Basin. The data, elicited through unstructured interviews from purposively selected informants, has been analysed thematically. The findings reveal that Egypt aspires to be a hegemon in the basin but is not. Despite its use of different coercive and subtle mechanisms to induce ideational or hegemonic compliance, these have not been successful: Ethiopia has not consented to or accepted Egypt’s claim over the Nile. Concomitantly, since the 1990s, Ethiopia’s position has transcended from veiled to overt contest, which anticipates a new order, challenging the monopolistic position of Egypt.

Employee ownership in China: new evidence

PurposeWith specific big-data mining worked on 61,522 firm announcements, we discovered a diverse Employee Share Ownership Plan (ESOP) model in China, called “Core-Staff-Based ESOPs.” Distinct from standard broad-based or executive-based ESOPs, these specific targeted-broad-based ESOPs require the qualification for participants, involving the participation of senior executives, directors at the middle level and any other employees that make particular contributions to firms. We take on the challenge to analyze ESOP mechanism, firm characteristics and performance in the view of organizational ecology and resource-based choice-making, and explore which factors have influenced the ESOP development in China.Design/methodology/approachWe utilize a combination of approaches including qualitative and quantitative methods, and construct the main database of 117,767 firm-quarter data.FindingsFirstly, based upon our institutional research, we find no coercive mechanisms that force all the Chinese listed firms to implement ESOPs since 2005. Secondly, our binary logistic regressions identify ESOP firms’ specific properties significantly distinct from non-ESOP firms, and draw profiles for these ESOP firms. Thirdly, our panel regression test results sustain the rational of ESOP mechanism, demonstrating that ESOPs enable Chinese firms to improve performance both in profits and their industry positions. Finally, with further quantitative tests, we find out this ESOP design’s limitations and the heterogenous effects due to China’s environments.Originality/valueThe discovery of Core-staff-based ESOPs contributes a diversity to the standard framework of ESOPs, enhances our understanding of China’s ESOP development, and provides new evidence for ESOP performance.

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.

High-coercivity nanocrystalline Nd-Fe-B powder regenerated from sludge via in-situ mechanochemical approach

The regeneration of Nd-Fe-B sludge is of great practical significance for achieving the sustainable development and recycling of rare earth elements. In this study, the in-situ regeneration of sludge was realized at a lower temperature of 850 °C via the mechanochemical approach based on ball-milling and Ca-reduction diffusion. Single-phase nanocrystalline magnetic powders with high coercivity were prepared by regulating the experimental parameters and rare earth elements. The grain size of Nd-Fe-B powder obtained by 5 wt% TbHx addition was 68.1 nm, with a high coercivity of 18.38 kOe. After purification and dehydrogenation, the coercivity was 6.68 kOe, and the coercivity mechanism was controlled by reverse magnetic domain nucleation. The low temperature in this study significantly reduced the energy consumption for the calcium reduction regeneration of sludge. It facilitated the preparation of nanocrystalline Nd-Fe-B powders with high coercivity, offering a new idea for recycling Nd-Fe-B sludge.

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.

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.

Grain boundary diffusion behaviors of hot-deformed magnets in different directions with additional pressure

The diffusion behaviors of hot-deformed magnets were investigated in two different directions with additional pressure. For magnets diffusion along the direction parallel to the C-axis (∥C magnets) and magnets diffused perpendicular to the C-axis (⊥C magnets), the coercivity increased by 3.66 kOe and 4.94 kOe, while the remanence decreased by 1.39 kGs and 1.04 kGs, respectively. The coercivity and remanence are both higher in ⊥C magnets as compared to ∥C magnets. SEM indicates that the orientation in ⊥C magnets is better than in ∥C magnets, which contributes to the more excellent remanence. The SEM also suggests the distribution of the rare-earth-rich phase was more uniform in ⊥C magnets. EPMA shows that the diffusion depth of ⊥C magnets reaches around 1500 μm, while ∥C magnets is less than 1250 μm. Both the homogeneous distribution of the rare-earth-rich phase and deeper diffusion depth are responsible for the improved coercivity of ⊥C magnets. EDS shows that the Nd70Cu30 preferentially entered the interior of the magnets through the interface formed by the fine grains of melt-spun ribbon edges for ∥C magnet during grain boundary diffusion process. But the ⊥C magnet did not show this preference during diffusion. The grain morphology and diffusion resistance of magnets in different directions is the fundamental cause for the difference of Cu distribution in ∥C magnet and ⊥C magnet. The initial magnetization curves suggests that the coercivity mechanism of the initial magnets combines nucleation and domain wall pinning, while the domain wall pinning is enhanced for the diffused magnets. The optimum performances with Br = 13.21 kGs, Hcj = 18.23 kOe, and (BH)max = 43.01 MGOe were achieved in ⊥C magnets.

The effect of Dy-Cu co-deposition and grain boundary diffusion on the microstructure and magnetic properties of sintered NdFeB magnets

In this paper, Dy-Cu coating was electrodeposited on the surface of commercial sintered NdFeB magnet as a diffusion source and the grain boundary diffusion was carried out on the sintered NdFeB magnet. The experimental results show that the coercivity of the diffusion magnet is increased from 993 kA/m to 1241 kA/m, an increase of 24.95 %, and the remanence is only reduced to 1.366 T, a decrease of 0.44 % compared with the original magnet. The electrochemical behavior analysis shows that with the addition of Cu2+, the reduction potential of Dy3+ appears a large positive shift, and the Dy-Cu co-deposition process is a three-dimensional instantaneous nucleation process. The SEM images show that the Dy-Cu deposition layer has a dense and flat surface with small grain size. The energy spectrum analysis shows that the Dy-Cu elements obtained by electrodeposition are uniformly distributed, and there is no massive agglomeration phenomenon. SEM-EDS line scan observation shows that the Dy elements diffused along the grain boundary phase mainly accumulate in the grain boundary phase and the epitaxial layer of the main grain. EPMA shows that Cu and Dy elements are evenly distributed in the grain boundary phase after grain boundary diffusion. SEM-BSE shows that the near-surface grain boundary phase structure is significantly optimized after grain boundary diffusion. XRD shows that Dy partially replaces the NdFeB main phase, leading to the migration of the main peak to the large angle direction. At the same time, due to the existence of low melting point metal, Dy preferentially enters the magnet internal, resulting in the decrease of the content of (Dy, Nd)2Fe14B phase. The optimization of the microstructure and grain boundary phase composition and the formation of (Dy, Nd)2Fe14B structure are the main reasons for the significant enhancement of the coercivity According to Kronmüller plots, the coercivity mechanism of diffusion magnet is still the magnetic domain nucleation inversion mechanism. After the Tafel test, it is found that the diffusion Dy magnet has a relatively positive corrosion voltage Ecorr and a relatively low corrosion current density Icorr, and its corrosion resistance is greatly improved.

Study of magnetization reversal and magnetic hardening in SmCo5 single crystal magnets

Large SmCo5 single-crystal spheres are used as simple model objects for both theoretical and practical studies of the coercivity mechanism in permanent magnets (PM). These samples exhibit coercivity values exceeding 1 T, achieved through the enhancement of surface smoothness. The morphology and magnetic results indicate that surface defects play a key role in the reversal mechanism and nucleation process. The reversal mechanism and coercivity are studied by means of different magnetization protocols, shedding light on the influence of two types of nucleus of reversal magnetic domains. We then utilize these objects to probe the angular dependence of coercivity. Our examination of samples with differing surface states reveals that enhanced surface smoothness corresponds to a behavior closer to the coherent rotation model. This study underscores the massive influence of surface defects on magnetization reversal. Thus, the reduction of imperfections in PM grain boundaries holds the potential to significantly increase the nucleation field and thus the coercivity. More generally, our study introduces a methodology for examining the magnetization reversal of permanent magnets using simple model objects.

New structural features and pinning-evolved coercivity mechanism: A potential route for developing high coercivities in anisotropic Sm-Fe-N material

Sm-Fe-N material holds immense promise as new material for developing next generation permanent magnets. However, the achievement of high coercivity in this material remains a big challenge, and moreover new coercivity theories beyond the commonly considered nucleation-type mechanism needs exploration. This study describes both the yielding of anisotropic Sm-Fe-N powders with high coercivities and the discovery of new coercivity mechanism by a systematic study using a designed milling preparation method. As a result, a random-direction cleavage behavior with unexpected XRD peak shifts and formation of new micron-sized flower-like particles were found in the yielded Sm-Fe-N powders. The grain sizes of the powders are of nanoscale dimension and they refine gradually as the milling time increases. The measured coercivity is up to 15.0 kOe, which is a substantial increase of approximately 36.4% compared to the original commercial powders and among the highest reported values via the milling preparation method (commonly below 13 kOe). The yielded powders also demonstrate a new dual-type coercivity mechanism (combing both nucleation-type and pinning-type control effect), and the improved pining effect contributes to the high coercivities. This study opens the door of utilizing pinning effect for achieving high coercivities in anisotropic Sm-Fe-N material.

Magnetization reversal and coercivity mechanism in ferrimagnetic M-type hexaferrite by controlling phase evolution

The correlation of phase evolution (annealing at different temperatures) with magnetic properties like magnetization reversal, coercivity mechanism, and energy product in M-type hexaferrite by substituting Sr in place of Ba has been reported in the present article. The Ba1-xSrxFe12O19 (x = 0.0, 0.5, & 1.0) have been prepared by the sol–gel auto-combustion method followed by annealing at different temperatures from 800 °C to 1200 °C. The structural and magnetic properties have been characterized by X-ray diffraction, Field emission scanning electron microscopy, Raman spectroscopy, and Vibrating sample magnetometer. The Rietveld refinement confirms contraction in unit cell parameters by replacing Sr in place of Ba and lattice expansion with increasing annealing temperature. There is no significant effect of substitution on magnetic properties found rather heat treatment affects greatly. The transition from a single domain to multidomain particles and their contribution to initial magnetization curves are analyzed. The differential susceptibility (dM/dH) calculated from room temperature magnetization confirms the existence of a pinning effect during magnetization reversal for samples heat treated below 1200 °C. Secondary phases or grain boundaries are believed to act like pinning centers. This work opens insight into the domain wall motion by microstructure engineering. The coercivity is tuned to 6.09 kOe by controlling the annealing temperature for the Ba1-xSrxFe12O19 (x = 1.0) sample. The maximum energy product (BH)max in the range of 0.94–1.27 MGOe has been achieved.

Analysis on coercivity enhancement mechanism of grain-boundary-diffused and Dual-alloyed Nd-Fe-B Magnets

With the rapid development of application fields, such as the green energy industry, has resulted in increased demand for magnetic characteristics, especially the coercivity (Hcj). In this paper, two types of (Nd, Dy)-Fe-B magnets with comparable Hcj values were prepared using by grain boundary diffusion (GBD) method and dual alloy (DA) method. The composition, microstructure, domain structure, and magnetization reversal process of GBD and DA magnets were subjected to comparison. Additionally, an analysis of the specific coercivity mechanism was also conducted by fitting the Brown's equation. The results of composition and microstructure analysis revealed the formation of core-shell structural grains were formed in both GBD and DA methods. Specifically, the GBD method exhibited a higher concentration of Dy in the shell, constituting 26.8 % of the total rare earth (RE) content. In contrast the DA magnets had Dy accounting for 15.8 % of the total RE content in the shell. This discrepancy was identified as the primary factor contributing to the superior efficiency in enhancing the coercivity (Hcj) observed in the GBD method. The fitting results showed that GBD magnets were more inclined to nucleate in the core region in grain, whereas DA magnets nucleate at the edge of the grain shell layer. Both the observation of magnetic domains and magnetization reversal processes analysis revealed that the demagnetization process in GBD magnets is more uniform, which leads to better squareness. Our finding can provide theoretical and experimental basis for the preparation of high-performance Nd-Fe-B magnets.

Nexus of circular economy R0 to R9 principles in integrated reporting: Insights from a multiple case study comparison

AbstractOver recent years, the Circular Economy (CE) has turned into a debated area worldwide as a way of achieving a more sustainable society. However, little is known about how companies can disclose CE‐related activities in their corporate reporting. This paper aims to explore how and to what extent CE‐related information is included in Integrated Reporting (IR) practices by promoting Sustainable Development Goals (SDGs). The study applies qualitative content analysis and thematic analysis approaches to explore the associations with CE, IR, the six capitals and SDGs. The institutional theory approach has been adopted to justify incorporating CE R‐principles activities into IR practices. Multiple case study findings demonstrate that every case company minimum one time cites the CE R principle, while case companies seen to be more involved in the reduce (R1), reuse (R2) and recycle (R7) are engaged with IR practices and focussing on SDGs. Whereas coercive, normative, and mimetic isomorphism mechanism substantially impacts CE activities concerning IR practices, we can argue that mimetic isomorphisms need further investigation because no structures and frameworks are available. In terms of managerial implications, this study proposed a combined framework of CE and IR that provides a conceptual picture of how CE activities intermesh with the IR framework and the six capitals, both essential for the Sustainable Development (SD) agenda participation and value creation process of companies.

Pledge and Forget? Testing the Effects of NATO’s Wales Pledge on Defense Investment

Abstract Do informal international agreements without coercive mechanisms affect states’ behavior? While scholars have long been interested in this question, answering it often poses empirical challenges, particularly in the arena of international security. By asking and answering a narrower question—Is NATO’s Wales Pledge on defense spending working?—I can empirically test the extent to which states have adhered to a public agreement without formal or coercive enforcement mechanisms. I argue that the Wales Pledge has led to higher spending because NATO the organization uniquely enables allies to influence one another’s defense planning, publicly and privately. I find support for this argument by interrogating disaggregated defense expenditures of NATO and EU members, and by comparing NATO allies Denmark and Norway with non-allies Finland and Sweden. Although the Wales Pledge has been maligned, it served its purpose by encouraging allies to spend more on defense, particularly on equipment modernization.