Coercivity Mechanism Research Articles

Coercivity mechanism of La–Nd–Fe–B films with Y spacer layer

The effect of the Y spacer layer on the phase composition, coercivity, and magnetization reversal processes of La–Nd–Fe–B films has been investigated. The addition of a 10 nm Y spacer layer increases the coercivity of the film to 1.36 T at 300 K and remains 0.938 T at 380 K. As the thickness of the Y spacer layer increases, Y participates in the formation of the main phase in the film, and further regulates the formation of La–B phases. The results of the first-order reversal curve (FORC) and micromagnetic fitting show that the coercivity of all the films is dominated by nucleation mechanism. The c-axis preferred orientation, good magnetic microstructure parameters and the largest dipole interaction enhance the coercivity. Therefore, the introduction of the Y spacer layer can be an effective way to improve the coercivity of La–Nd–Fe–B film over a wide temperature range of 150 K–380 K.

Electrodeposition of Dy and its grain boundary diffusion behavior of sintered NdFeB magnets

This paper presents the electrodeposition of a Dy layer onto the surface of sintered NdFeB magnets to serve as a diffusion source. Subsequently, the sintered NdFeB magnets were subjected to grain boundary diffusion treatment through electrochemical deposition at the solution temperature of 45 °C and the solution pH (hydrogenii) of 4.0. The results indicated that the coercivity of the Dy-diffused magnet increased from 1073 kA/m to 1418 kA/m compared to the original magnet after annealing at a primary diffusion heat treatment temperature of 900 °C for 6 h and subjected to the same secondary tempering heat treatment at 500 °C for 2 h, while the remanence remained relatively unaffected. SEM (Scanning Electron Microscopy) revealed that the Dy coating exhibited a compact and flat surface with a small grain size. Energy spectrum analysis confirmed a relatively uniform distribution of Dy elements in the electrodeposition coating, without any significant agglomeration. SEM-EDS (Scanning Electron Microscopy-Energy Dispersive Spectrometer) line scan demonstrated that the diffused Dy elements along the grain boundary phase primarily concentrated in the grain boundary phase itself and the epitaxial layer of the main grains. BSE (Backscattered Electron imaging) revealed the presence of a thin and continuous grain boundary phase structure between the main phases following grain boundary diffusion. XRD (X-ray diffraction) analysis demonstrated a general shift toward higher angles in the main peak of NdFeB after Dy diffusion. The remarkable increase in coercivity of the diffused Dy magnets can be attributed to the optimization of microstructure, grain boundary phase composition, and the formation of the (Dy,Nd)2Fe14B structure. The coercivity mechanism in diffusion Dy magnets was still governed by a nucleation reversal mechanism, as supported by the Kronmüller-Plot curve fitting. Tafel tests have revealed that Dy-diffused magnets have a much higher corrosion resistance with a more positive equilibrium potential, Ecorr, and a lower corrosion current density, Icorr.

The Field-Dependent Magnetic Viscosity of FeNdB Permanent Magnets.

The time-dependent decrease of the magnetic polarization of magnet materials in the presence of an opposing field is well known as the magnetic viscosity or magnetic aftereffect. In previous studies, magnetic viscosity was usually measured in fields when in the vicinity of coercivity HcJ, and this was conducted in order to understand the coercivity mechanism in magnetic materials. In this study, the magnetic viscosity of commercial FeNdB magnets is determined at opposing fields weaker than HcJ and at different temperatures in the range from 303 to 433 K (i.e., from 30 to 160 °C) by means of a vibrating sample magnetometer (VSM). As a result, the parameter Sv, which describes the magnetic viscosity in the material, was found to increase with increases in the opposing field. Furthermore, both the parameter Sv and its dependence on the temperature were found to correlate with the coercivity HcJ of the material. Also, a difference with regard to the parameter Sv for the materials measured in this study with similar magnetic properties, but which had undergone different types of processing, could not be found. Knowledge of the field- and temperature-dependent behavior of the magnetic viscosity of FeNdB magnets allows for better estimations over the lifetime of a component under operating conditions with respect to the magnetic losses in FeNdB magnets that are used in electric components.

EFFECT OF INSTITUTIONAL FORCES ON THE INTENTION TO ENGAGE IN RAINWATER HARVESTING IN TANZANIA

This study examined the effect of institutional forces on intention to engage in rainwater harvesting in Tanzania, East Africa. The study aimed to examine specifically, (i) the effect of coercive mechanism on intention to engage in rainwater harvesting, (ii) the effect of mimetic mechanism on intention to get involved in rainwater harvesting and (iii) the effect of normative mechanism on intention to engage in rainwater harvesting. A quantitative type, explanatory research design and random sampling were applied by this study. The study collected data using structured questionnaire to 390 community members. Data analysis involved the application of descriptive and multiple linear regression analysis through the employment of IBM SPSS. The results indicated a positive and significant effect of institutional forces on the community’s intention to engage in rainwater harvesting. The present study concludes that coercive, mimetic and normative mechanisms are predictors of the intention to engage in rainwater harvesting by the Tanzanian community. Hence, it is recommended that executives, investors, ministry of water and irrigation and other water stakeholders in Tanzania should strategically apply institutional forces

A Difusão das Comissões de Heteroidentificação nas Universidades Públicas: Instituições e Mudança Organizacional

Abstract This article draws insights from the literature on institutional isomorphism and social movements theory to explain the diffusion in Brazil of procedures for validating the self-identification of candidates for admission to federal universities through racial quotas. The diffusion of these procedures has transformed how the right to affirmative action is understood and how it has led to organizational challenges. By analyzing documents and interviews, this article identifies the coercive, mimetic, and normative mechanisms at play. It shows that they derived from interactions among Black university students, staff, faculty members, and organizations of the black movement and state agencies, all engaged in protecting racial affirmative action. Implications for studying change in Brazil’s higher education and race relations are also discussed. Higher education and race relations in Brazil are also discussed.

ASEAN REGIONAL FORUM AS A COOPERATIVE SECURITY MECHANISM

The article explores the ASEAN Regional Forum (ARF) as a pivotal cooperative security framework in Asia-Pacific. Cooperative security, characterized by multilateralism, inclusiveness, transparency, and consensus-building, underpins the ARF’s functioning. The study delves into the ARF’s establishment during the post-Cold War era, highlighting ASEAN’s political and diplomatic gains, which fostered trust among major powers and regional actors. The authors analyse the ARF’s development, noting its primary focus on confidence-building measures, reflecting the principles of non-interference and consensus inherent in ASEAN’s norms. Key findings indicate that while the ARF has made strides in enhancing regional security dialogue, it remains constrained by its slow-moving approach to preventive diplomacy and the lack of coercive mechanisms. The Forum's ability to address traditional security challenges, such as the North Korean nuclear threat and the South China Sea dispute, is limited. Therefore, the ARF focuses on addressing non-traditional security issues, including counterterrorism and disaster mitigation. The findings show that ARF's role encompasses extending ASEAN’s cooperative security norms to the broader Asia-Pacific region, promoting transparency and fostering a collaborative security environment by means of confidence-building measures. The article posits that while ASEAN’s leadership in the ARF is more an outcome of regional circumstances than deliberate strategy, the ASEAN Regional Forum remains an important mechanism for security cooperation in Asia-Pacific.

High coercivity in Sm-doped SrFe12O19 powders with spherical morphology prepared by ultrasonic spray pyrolysis

SrFe12O19 is widely used due to its low cost, stability and corrosion resistance. In this study, Sm-doped porous SrFe12O19 powder with high coercivity was synthesized using KCl-assisted spray pyrolysis. The Sm doping, microstructure and magnetic properties were studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and vibrating sample magnetometer (VSM). The results showed that when Sm-doping amount was 0.2, the ferrite powder prepared by KCl-assisted spray pyrolysis had high coercivity of 7.286 kOe and saturation magnetization of 56.422 emu/g. The coercivity of the Sm-doped samples increased by 39.23 % compared with that of the undoped samples. The significant increase in coercivity was associated with the improvement of super-exchange interaction between Fe3+ particles caused by Sm doping, and the size decrease of the hexagonal plate Sr-ferrite particle caused by KCl action. The influencing mechanism of coercivity was discussed in detail based on the analysis of crystal structure and microstructure observation.

Investigation into the role of Co doping in the microstructure and magnetic characteristics of nanocrystalline Nd-Ce-La-Fe-B alloys

In this study, [Nd0.5(Ce0.5La0.5)0.5]17Fe78-xCoxB6 (x = 0 ∼ 1.5 at. %) ribbons are prepared via a direct melt-spun (wheel speed of 28 m/s). The impacts of Co doping on the crystal structure, Curie temperature Tc, magnetic parameters (Br, Hci and (BH)max) of [Nd0.5(Ce0.5La0.5)0.5]17Fe78-xCoxB6 alloys are systematically assessed. X-ray diffraction patterns and Rietveld refinement data demonstrate that the exclusive presence of a pure hard magnetic 2:14:1 phase without any secondary phases across all samples. Compared with Co-free sample (x = 0), the Br, Hci and (BH)max of Co-doped with x = 1 are increased by 15.0 %, 4.6 % and 42.9 %, respectively. The coercivity mechanism in the [Nd0.5(Ce0.5La0.5)0.5]17Fe78-xCoxB6 alloys arises from the integration of reversed domain nucleation and robust pinning of domain walls. The magnetic domain structure and quantitative analysis based on the microstructure and demagnetization behavior are conducted to investigate the exchange coupling interactions among the 2:14:1 grains. This exploration reveals that the enhanced magnetic properties stem from the refinement of the 2:14:1 phase's grains, leading to more uniform and smaller interaction domains.

Ti‐Doped Nanocomposite Pr2Fe14B/α‐Fe Ribbons with High Coercivity

Nanocomposite permanent magnetic alloys are prepared by the melt‐spinning technique with wheel speed ranging from 21 to 33 ms−1. X‐ray diffraction results show that the as‐spun ribbon is rich of soft α‐Fe, hard Pr2Fe14B magnetic phases, and no other metastable phases are found in our alloy ribbon. Initial magnetization curves reveal that the coercivity mechanism of the ribbons vary with the content of Ti. For x = 2, coercivity is mainly determined by pure pinning; while for x = 1, 3, and 4, it is mainly controlled by the mixture of nucleation of domain and localized pinning at grain boundaries. The coercivity value of 1026 kA m−1, the highest value reported so far, is mainly generated from a pure pinning mechanism in the ribbon with x = 2. The recoil permeability shows a minimum value range from to for x = 2 alloy, suggesting strong exchange coupling between the magnetic grains and then leading to the concurrent reversal of soft and hard phase grains during the demagnetization process. The Henkel plots demonstrate only exchange interaction for x = 1 and exchange interaction with slightly magnetostatic interaction for x = 2, 3, and 4. The exchange interaction exhibits maximum strength for x = 2, which is the reason for high coercivity.

A systematic investigation of Pr-rich Pr-(Fe,Co)-B material system: Phase formation, microstructure and magnetic property

Praseodymium (Pr) doping is known to increase the coercivity of Nd-Fe-B permanent magnets without significant reduction in magnetization. However, there is still a lack of studies on the specific impact of Pr in comparison of Nd on phase formation and microstructure, which is crucial for the development of high-performance Pr-based magnets. In this study, we investigate the phase formation, microstructure, magnetic properties and coercivity mechanisms in Pr-rich Pr15(Fe1-xCox)78B7 (x = 0 – 1) alloys using advanced synthesis, high-resolution electron microscopy, and modeling techniques. The alloys with x = 0 and 0.2 are comprised of a Pr2(Fe,Co)14B matrix phase with a non-magnetic Pr-rich intergranular phase, and this microstructure is stable up to 1150 °C. Due to the Pr-rich phase, the magnetization reversal in Pr2(Fe,Co)14B grains is hindered, resulting in high coercivity of 1.8 ∼ 2.0 T. For the Co concentration of x = 0.4 - 0.8, the Pr-rich intergranular phase gradually disappears, and ferromagnetic Pr(Fe,Co)4B, Pr(Fe,Co)2 or Pr(Fe,Co)3 phases are exist instead. The soft-magnetic Pr(Fe,Co)2 phase acts as a weak link and tends to induce the nucleation of the reversal interaction domain inside the Pr2(Fe,Co)14B grain near the Pr(Fe,Co)2 / Pr2(Fe,Co)14B interface, resulting in degraded coercivity of 0.7 ∼ 1.0 T. In the Pr15Co78B7, the Pr2Co14B, PrCo4B and PrCo5 phases co-exist as independent exchange-coupled grains and the weak link was found at the PrCo4B / Pr2Co14B interface, where the reversal interaction domains nucleate and then propagate into Pr2Co14B grains, resulting in a coercivity of approximately 1.2 T. Our experimental findings were compared with micromagnetic modeling, which reveals that the change in the direction of magnetization at the interfaces of exchange-coupled grains often has a very complex topology, and the transition regions between two interaction domains is “pinned” at the structural inhomogeneities. Thus, by using the Pr-Fe-Co-B alloys as a model system, we highlight the significance of gaining a deeper understanding of these processes at the micro- and nano-levels. This knowledge may assist in constructing more accurate models of magnetization reversal in nanocrystalline magnets.

Coercivity mechanism of high-performance anisotropic heterostructure SmCo5 magnets

Due to its large magnetocrystalline anisotropy field and high Curie temperature, SmCo-based magnets are irreplaceable in high-temperature applications. The hot-deformed SmCo-based magnets are especially attractive for their excellent corrosion resistance, making them more suitable for harsh environments. However, it is still challenging for hot-deformed SmCo-based magnets to obtain high magnetization and high coercivity simultaneously. Therefore, it is necessary to analyze the relationship between its microstructure and magnetic properties and explore its magnetic hardening mechanism to guide the further improvement of magnetic properties. In this paper, the anisotropic heterostructure SmCo5 magnet was prepared by combining large height-reduction and introducing a nano-grained Sm-rich phase. Strong c-axis texture, (BH)m of 16.1 MGOe, and Hci of 9.6 kOe were obtained via the heterostructure with SmCo5 micron-grain and Sm-rich nano-scale precipitates. The magnetic domain observation and technical magnetization analysis demonstrate that the coercivity mechanism is dominated by nucleation. The results also show that the smooth and Sm-rich precipitated grain boundary provides weak pinning effects. It provides a reference for the development of high-performance nanocrystalline SmCo5 magnets.

Safety and function of programmable ventriculo-peritoneal shunt valves: An in vitro 7 Tesla magnetic resonance imaging study.

The quantity of ultra-high field MRI neuroimaging studies has rapidly increased. This study tests function, safety, and image artifacts of two frequently implanted programmable ventriculo-peritoneal (VP) shunt valves in a 7T MRI system. All tests were performed using a whole-body 7T MRI system. Three proGAV 2.0 and 3 CODMAN CERTAS® Plus programmable VP-shunt valves were tested in three steps. 1) Deflection angle tests close to the bore opening at the location of a static magnetic field gradient of 3-5 T/m. 2) Valves were fixed on a spherical phantom in 3 positions (a. lateral, b. cranial, c. cranial with 22.5° tilt anteriorly) and assessed for keeping the programmed pressure setting and reprogrammability. 3) Valves were fixed on the phantom and positioned lateral in a radiofrequency head coil. MRI scans were performed for both models, including MPRAGE, GRE and SE sequences. Deflection angles were moderate (13°, 14°, 13°) for the proGAV valves and close to critical (43°, 43°, 41°) for the CODMAN valves at the test location. Taking a scaling factor of 2-3 for the maximum spatial magnetic field gradient accessible to a patient within the magnet bore into account renders both valves MR unsafe regarding ferromagnetic attraction. The proGAV valves kept the pressure settings in all positions and were reprogrammable in positions a. and b. In position c., reprogrammability was lost. The CODMAN valves changed their pressure setting and reprogrammability was lost in all positions. MR image signal homogeneity was unaltered in the phantom center, artifacts limit the assessability of structures in close vicinity to the valves. Both tested programmable VP-shunt valves are MR unsafe for 7T systems. Novel programming mechanisms using permanent magnets with sufficient magnetic coercivity or magnet-free mechanisms may allow the development of programmable VP-shunt valves that are conditional for 7T MR systems.

Unveiling the origin of the large coercivity in (Nd, Dy)-Fe-B sintered magnets

Nd-Fe-B-based permanent magnets are widely used for energy conversion applications. However, their usage at elevated temperatures is difficult due to the relatively low coercivity (Hc) with respect to the anisotropy field (HA) of the Nd2Fe14B compound, which is typically 0.2HA. In this work, we found that the coercivity of an (Nd0.8Dy0.2)-Fe-B sintered magnet could reach 0.4HA, which was twice as high as the Hc/HA of its Dy-free counterpart. Detailed microstructural characterizations, density functional theory and micromagnetic simulations showed that the large value of coercivity, Hc = 0.4HA, originated not only from the enhanced HA of the main phase (intrinsic factor) but also from the reduced magnetization of the thin intergranular phase (extrinsic factor). The latter was attributed to the dissolution of 4 at.% Dy in the intergranular phase that anti-ferromagnetically coupled with Fe. The reduction in the magnetization of the intergranular phase resulted in a change in the angular dependence of coercivity from the Kondorsky type for the Dy-free magnet to the Stoner–Wohlfarth-like shape for the Dy-containing magnet, indicating that the typical pinning-controlled coercivity mechanism began to show nucleation features as the magnetization of the intergranular phase was reduced by Dy substitution.

The Implicit Social Contract in Soviet Higher Education and Its Transformation in the 1990s

The article presents a theoretical analysis and characterizes the parameters of the implicit social contract between society and the intelligentsia during the latter part of the Soviet period. The specificity of this type of implicit social contract is demonstrated, particularly regarding the potential benefits and existing limitations in pursuing higher education and realizing the life ambitions of the Soviet intelligentsia. The archetypes and behavioral strategies of individuals during the Soviet era are examined, both in terms of socially accepted and deviant conduct. The institutional elements that shape the experiences of individuals with higher education during the Soviet period are described, specifically the influence of officially proclaimed morality, ethical norms, and coercive mechanisms as value systems. The issue of the overproduction of individuals with higher education is highlighted, which resulted in the devaluation of its significance and a decline in social status for the technical intelligentsia during the Soviet period. The problems surrounding the quality of primary and higher education in the USSR are discussed, and the factors contributing to its crisis in the late USSR are identified. The transformation of values in the post-Soviet period is examined, and some consequences stemming from this transformation are explored.

Tunable magnetic properties and magnetic domain structure of nanocomposite permanent materials via Ti addition into Nd-Fe-Co-B alloys

In this work, the effect of tunable Ti content on the microstructure, magnetic domain structure, and magnetic properties of as-spun and annealed Nd9.5Fe79-xCo5TixB6.5(x = 0,1,2,3,4) alloys at the quench speed of 18 m/s were investigated. For the as-spun alloy, augmenting the Ti content enhanced the initial crystallization temperature and the stability of the amorphous phase. Simultaneously, the incorporation of Ti led to augmentation in the quantity of nanocrystals within the amorphous matrix, thereby facilitating the formation of vortex-like magnetic domains with large size but reduced the saturation magnetization Ms. For the annealed alloy, the incorporation of Ti inhibited the precipitation of α-Fe phase, refined the grain, enhanced the exchange coupling between the soft and hard magnetic phase and facilitated the formation of smaller, more uniform vortex-like magnetic domains, These alterations were beneficial to improve the comprehensive magnetic properties. Furthermore, the addition of tunable Ti resulted in a remarkable impact on coercivity enhancement. The coercivity value exhibited a significant increase of 54.30%, surging from 374.24 kA/m to 577.51 kA/m. Upon a thorough analysis of the magnetic domains and coercive force mechanisms, it was ascertained that the introduction of Ti substantially augmented the creation of vortex-like domains. These domains effectively impede domain motion, consequently elevating the material's coercivity.

Religion as a Means of Political Conformity and Obedience: From Critias to Thomas Hobbes

This study identifies common perceptions between Thomas Hobbes’ approach to religion with that of Critias the sophist. Despite the distance that separates the social environments within which each of these authors lived and wrote, in their political philosophy we can spot a shared set of concerns, whose importance transcend the historical and political contexts in which the authors lived and wrote: in the state of nature, where no organized commonwealth (or civil society) exists, capable of repressing the innate greed of men and women, savagery and conflict reign supreme; life is threatened by violence and extreme aggression. It is only the state of society that guarantees stability and good life. For both thinkers, belief in immaterial spirits protects the state of society; belief in God promotes obedience to civil law and guarantees human co-existence. In Critias’ mind, religion is a necessary means to avert aggression, even when the State’s executive powers are unable to punish offenders, using all necessary tools to prevent hostility and conflict. While civil law is the hallmark of peace and stability, belief in a transcendent entity that influences collective and individual modes of living, is an important addition to the pursuit of social peace. A few centuries later, Hobbes (influenced by the misery of the English Civil War) developed viewpoints that also highlight the role of religion in defending social peace. Nonetheless, in Hobbes’ mind religion could safeguard stability only (A) when ecclesiastical authorities submit to the judgment of an omnipotent Sovereign and (B) when the coercive mechanisms of the State supress religious pluralism, prohibiting different interpretations of the Bible, which Hobbes himself considered one of the main causes of conflict.

Direct observation and stochastic analysis on thermally activated nucleation and growth of individual magnetic domain

The nucleation and subsequent growth of the reversed magnetic domain at a finite temperature are stochastic processes, which are often analyzed using an ensemble of magnetic elements. In this study, we investigate the stochastics of magnetization reversal in multiple trials for the sole magnetic domain. Specifically, we utilize the robust magnetic domain structure formed in a dual-exchange-biased Pt/Co/Au/Cr2O3/Pt thin film. Our investigation encompasses the latency of reversed domain nucleation and the subsequent domain wall motion based on time-lapse magnetic domain observations. The time evolution of the magnetic domain is observed after applying a pulsed magnetic field superimposed on a DC field. Magnetization reversal is triggered by the nucleation of a small embryo with finite latency, followed by domain wall propagation. The nucleation probability of the embryo increases exponentially with the DC field, thus indicating that the nucleation process obeys the Poisson process. An analysis of the relaxation time for nucleation provides a suitable expression for the energy barrier. The nucleated domain wall propagates with temporal stops, thus indicating creep motion. The temperature dependence of the relaxation time and domain wall creep motion reveal that the magnetic anisotropy in the antiferromagnetic layer significantly affect both the energy barrier for nucleation and the depinning potential of domain wall propagation. This study provides comprehensive understanding into the coercivity mechanism and contributes to the thermal stability of magnetic/spintronic devices.

High-performance anisotropic SmCo-based magnet with novel microstructure

A novel microstructure of magnetically anisotropic SmCo-based magnet with high-performance is reported. The magnet consists of SmCo7-H (TbCu7-hexagonal type), Sm2Co17–H (Th2Ni17-hexagonal type) and SmCo3-R (SmCo3-rhombohedral type) phases. The maximum magnetic energy product of the magnet is 231.69 kJ/m3, and the intrinsic coercivity is 1005.47 kA/m. An outstanding intrinsic coercivity temperature coefficient (β) of −0.125%/K between 298 and 773 K is obtained, which is very close to the β of commercial high-temperature Sm2Co17-based sintered magnets. The initial magnetization curve indicates that the coercivity mechanism is controlled by a domain wall pinning mechanism. The SmCo3-R lamellar phase may be a potential pinning center or self-pinning center. The microstructure of the magnet is different from that of any previous SmCo-based magnets. These findings provide a new idea for preparing high-performance SmCo-based permanent magnets.

Atomic‐Scale Transition Zones Determined Coercivity in Samarium‐Cobalt Based Permanent Magnets

AbstractSmCo‐based permanent magnets with nanocellular structure exhibit significant advantage for high‐temperature applications. Due to the lack of experimental intrinsic magnetic parameters and unclear nanocellular interface, a fully understanding on coercivity mechanism is still limited. Here the intrinsic magnetic properties of designed two single‐phase alloys representing nanocellular structure at various temperatures are acquired. Using 3D atom probe and high‐angle annular dark‐field scanning transmission electron microscopy, the existence of the nanoscale transition zones located at nanocellular interface is revealed. Moreover, the transition zones exhibiting high magnetocrystalline anisotropy is found to contribute dominantly to the coercivity. The calculated coercivity via micromagnetic simulation considering transition zones agrees well with the tested coercivity at various temperatures. This knowledge deepens the fundamental understanding on coercivity mechanism.

Magnetization reversal and coercivity mechanism in truncated conical nanowires of permalloy

Magnetization reversal and coercivity mechanism in truncated conical nanowires of permalloy