Search Results (465)

Rare-earth-based permanent magnets are key elements for today’s technologies. Their recycling is crucial for securing the supply of critical raw materials and ensuring a sustainable circular economy in magnet production. In this study, hydrogen decrepitated NdFeB powders recovered from end-of-life magnets were processed using planetary ball milling to obtain powders suitable for recycled magnet production. The magnets were sourced from a wind turbine, scooter motor, and ring magnet, and exhibit different compositions and properties. The structural, morphological, and magnetic properties of the hydrogenated and ball-milled powders were investigated considering the effects of the milling time and ball diameters. Submicron-sized powders were achieved within 10 min with 5 mm balls, while longer milling times were required to obtain similar particle size reduction with 10 mm balls. Milling resulted in structural damage to the hydrogenated powders. Furthermore, although milling decreased the magnetization of the powders, an increase in the coercive field was observed for certain milling times. Micrometric powders sourced from the wind turbine, milled for 10 min using 5 mm balls, exhibited the highest coercive field of 0.27 T. This behavior is discussed considering the effect of the particle size reduction, the structural damage, the particle agglomeration, and the local compositional changes. We conclude that the powders produced from different source magnets exhibit similar patterns of morphological, structural, and magnetic changes under milling, and only the Tc and the Hc of the powders depend on their original magnet. Ball milling represents a promising technique for particle size refining in the hydrogen processing of magnetic scraps, a crucial step in the magnet-to-magnet recycling process. Full article

Digital fluxgate magnetometers have been widely used in deep space exploration due to their low noise, high sensitivity, and high reliability. This paper presents a digital fluxgate magnetometer using a fifth-order single-loop 1-bit Sigma–Delta modulator. With a consistent system structure, measurement range, test setup, and calculation method, the characteristics of magnetic field measurement noise and non-linear error are obtained under four OSR configurations through simulation analysis and experimental testing. The test results show that within the range of ±65,000 nT, the system achieves its optimal performance with a non-linearity of 0.024%, an RMS noise of 0.106 nT, and a noise power spectral density of 5.7 pT·Hz^−1/2 at 1 Hz. These results indicate that increasing the OSR can effectively improve the performance of this digital fluxgate magnetometer, enabling high linearity and low noise measurement in Earth’s magnetic field. Full article

Ultralight bosonic dark matter (UBDM) that couples to electromagnetism can generate an oscillating magnetic-field signal at the Earth’s surface. This is referred to as the “Earth transducer” effect, as the Earth converts UBDM into a detectable magnetic field. Similar DM-induced fields in laboratory experiments typically scale with the size L of the experiment. Because the Earth transducer signal instead scales with the large radius of the Earth, R, it is one of the most powerful direct probes of UBDM with masses $m_{\mathrm{DM}}\lesssim 1/R\sim 3\times {10}^{-14}\mathrm{eV}$. It has many other favorable properties, such as high spatial and temporal coherence and robustness to atmospheric modeling. In this review, we derive the Earth transducer effect and its properties for multiple UBDM models, and we discuss current and future prospects to detect it. Full article

Nanocomposite rare-earth permanent magnets composed of exchange-coupled hard magnetic nanoparticles offer a promising route toward high-performance, rare-earth-efficient magnet technologies. In this work, we investigate the structural self-organization and magnetic hysteresis behavior of 40 nm Sm₂Co₁₇/Nd₂Fe₁₄B hybrid nanoparticles using a combined molecular dynamics (MD) and micromagnetic simulation framework. First, MD simulations are employed to study the Brownian motion and field-induced assembly of the hybrid nanoparticles at two particle concentrations (1 and 5 mg/cm³). In the absence of an external magnetic field, the nanoparticles display dispersed configurations governed by thermal fluctuations and interparticle interactions. Upon application of a high magnetic field (500 mT), the particles align into linear chain-like assemblies, with a more pronounced and rapid aggregation at higher concentration. Subsequently, micromagnetic calculations performed using the OOMMF are used to determine the magnetization reversal behavior of the assemblies. Quasi-static hysteresis loops at low field (40 mT) and room temperature reveal enhanced coercivity and remanence for field-aligned chain structures compared to randomly oriented particle ensembles. Additionally, increasing particle concentration amplifies the field-induced collective response due to stronger dipolar coupling. The combined MD–micromagnetic approach provides insight into structure–property relationships in magnetic nanocomposite systems and highlights the critical role of particle arrangement and concentration in determining magnet performance. These results contribute to the design principles for advanced nanostructured permanent magnets with tunable magnetic anisotropy and energy density. Full article

Magnetometers are essential for monitoring the Earth’s magnetic field in applications such as geophysics, space weather, navigation, and volcanic studies. While professional-grade instruments provide high reliability, their cost limits spatial coverage, particularly in remote regions. This study presents a comparative analysis of five ground-based magnetometers deployed simultaneously at Universidad Adventista de Chile (36.64° S, 71.99° W) from 5–8 August 2025. Noise, signal stability, and response to geomagnetic variations were evaluated, emphasizing the influence of ambient temperature. Fluxgate and subsurface-deployed instruments showed higher consistency and reduced thermal sensitivity, while low-cost magneto-inductive sensors exhibited strong linear temperature dependence, sometimes with temporal delays. Inter-instrument correlation analyses highlighted performance differences and the trade-offs between cost and reliability. The results demonstrate that low-cost magnetometers, if carefully deployed and calibrated, can complement professional-grade sensors, improve spatial coverage, and provide valuable geomagnetic observations in regions with limited infrastructure and logistical constraints. Full article

Wound Field Synchronous Motors (WFSMs) offer precise control over the rotor magnetic field, making them well suited to electric vehicle (EV) traction applications that require adjustable excitation, wide constant-power operation, and freedom from rare-earth permanent magnets. The excitation system (ES) governs the rotor field strength and therefore directly influences motor efficiency, dynamic response, and operational stability. This paper reviews modern excitation strategies for WFSMs in EV traction, with particular emphasis on contactless approaches based on wireless power transfer (WPT). The fundamental principles of inductive power transfer (IPT) and capacitive power transfer (CPT) are presented, together with their design considerations, compensation topologies, power electronic interfaces, control strategies, and practical challenges, followed by a discussion of hybrid IPT–CPT systems. Representative experimental studies in each category are compared on the basis of power level, efficiency, operating frequency, and misalignment tolerance. A capacitive power coupler is also designed for a WFSM, which requires a 6-amp DC field current, where the geometry of the coupler is constrained by the WFSM rotor geometry. The review identifies open challenges—including misalignment sensitivity, electromagnetic interference, thermal constraints, and air-gap variability under rotation—and outlines research directions for compact, efficient, and reliable WPT-based excitation systems for next-generation EV traction motors. Full article

Analysis of variations in the components of the Earth’s magnetic field, recorded at the magnetic observatory of the Institute of Ionosphere (Almaty, Kazakhstan) during the earthquakes of 22 January 2024 and 4 March 2024, showed that these fluctuations were not related to intrinsic variations in the magnetic field itself, but rather to mechanical oscillations of the magnetometer together with its support. Evidence supporting the seismokinetic origin of the variations in the vector magnetometer was the discrepancy between the total magnetic field measured by the absolute magnetometer and the total magnetic field calculated from the vector magnetometer readings. Equations were derived that relate variations in the components of the magnetic field to the tilt angles of the sensor, enabling the determination of the direction of arrival of seismic shock waves. Azimuths of earthquake epicenters were calculated from oscillations observed in magnetogram records for several events, and these were compared with azimuths obtained from a network of seismic stations. It is shown that, in order to improve the accuracy of geomagnetic field measurements—required for the study of seismoelectric and seismomagnetic phenomena, as well as for identifying earthquake precursors—the design of magnetic observatories should be supplemented with an inclinometer to enable correction of vector magnetometer measurement results. Full article

The particular microstructure of hot-deformed Nd-Fe-B magnets leads to difficulties in finding a direct recycling route. In this work, a combination of field-assisted sintering technology/spark plasma sintering (FAST/SPS) and spark plasma texturing (SPT) is used as pre-compaction and deformation techniques, respectively, for the consolidation of crushed, hot-deformed Nd-Fe-B scrap. Field-assisted sintering has the unique advantage of maintaining fine microstructures during material densification, making it an ideal candidate for direct recycling of this material. Recycled magnets, made from 100 wt% crushed magnet scrap, were able to achieve energy products of over 200 kJ m⁻³ after FAST/SPS pre-compaction and SPT deformation. These recycled magnets could then be smoothed and cut to the size of industrial bar magnets for testing in the motor of a water pump. When tested, the recycled magnets could achieve 95% of the electromotive force compared to industrial standard magnets. Full article

AMn₇O₁₂ perovskites (with A = divalent elements) show complex structural and magnetic transitions including incommensurate orbital density waves and coupled/decoupled modulated spin helicity originating from charge-ordered Mn³⁺/Mn⁴⁺ cations with the 3:1 ratio at the B perovskite sites and unusual apically compressed Jahn–Teller distortions of MnO₆ octahedra. The same Mn³⁺:Mn⁴⁺ ratio can be achieved in RCuMn₆O₁₂ compositions, where R is a trivalent rare-earth cation. Therefore, the comparison in behavior of AMn₇O₁₂ and RCuMn₆O₁₂ is of interest. In this work, the A-site-ordered quadruple perovskite NdCuMn₆O₁₂ was prepared by a high-pressure high-temperature method. Its structural properties were investigated by synchrotron powder X-ray diffraction between 100 K and 350 K and laboratory powder X-ray diffraction between 5 K and 300 K. It shows a first-order structural phase transition from Im-3 symmetry (at high temperatures) to R-3 symmetry near 292 K. The structural transition is accompanied by charge (Mn³⁺/Mn⁴⁺) and unusual orbital (on the Jahn–Teller active Mn³⁺ cations located in MnO₆ octahedra) orders. However, no additional structural/orbital modulations were found at lower temperatures in comparison with AMn₇O₁₂. Magnetic properties were investigated by temperature- and field-dependent magnetization and specific heat measurements, where a ferrimagnetic transition was found near 120 K. In addition, low-temperature magnetic anomalies were observed near 20 K, probably originating from the Nd sublattice. Full article

Gadolinium is a rare-earth element that is promising for the field of biomedicine due to its unique properties that enhance image quality, giving it high potential in targeted cancer therapy, antimicrobial treatments, etc. The disadvantage of Gd-containing materials is their high toxicity. In this work, ensembles of Fe and Al₂O₃ nanoparticles were fabricated by the electric explosion of wire and Gd ribbons using rapid quenching techniques. Stable Fe, Fe/Gd and Fe/Gd/Al₂O₃ aqueous suspensions with a Z-potential of about −54 mV were fabricated by the ball-milling mechanosynthesis of Fe (100%), Fe and Gd (70 and 30 wt. % accordingly) and Fe, Al₂O_3, and Gd (69, 30 and 1 wt.% accordingly). Fillers from suspensions were used for the synthesis of epoxy composites mimicking natural tissue with embedded magnetic particles. The concentration range for synthesized epoxy composites (0, 5, 10, and 15 wt.% of the filler) corresponded to the biomedical range of interest. Thin-film magnetoimpedance (MI) elements were prepared by a sputtering technique: conventional [FeNi/Cu]₅/Cu/[Cu/FeNi]₅ (NP) element and [FeNi/Cu]₅/Cu/[Cu/P{FeNi]₅} element with patterned top multilayer (SqP). They showed a maximum MI ratio of about 160% for NP and about 60% for SqP. MI sensor response was affected by the presence of filled magnetic composites in the shape of cylinders (5 mm × 4 mm) situated at about 1 mm due to the stray fields in the filler. MI response showed a linear dependence on the filler concentration for each selected position. These results open the possibility to develop new iron- and gadolinium-containing materials for simultaneous magnetic imaging and detection by magnetic field sensors, extending the functional properties of Fe/Gd materials for biomedical devices and therapies. Full article

Synchronous machines used in wind turbines typically use rare earth permanent magnets (PMs) due to the possibility of high power densities and efficiencies. However, alternative non-PM topologies are gaining popularity due to the cost and supply volatility of PMs. Wound-field flux-switching machines (WFFSMs), although boasting high torque densities and being PM-free, have lower power densities than PM machines. However, a double-stator wound-field flux-switching machine (DSWFFSM) exemplifies even greater power density. This study investigates the application of DSWFFSMs for direct-drive wind applications. Furthermore, the performance of an optimized 3 MW DSWFFSM design is compared with a single-stator WFFSM design. Both designs are based on the volume of a single-stator PM flux-switching machine from the literature. Although the torque per weight for the DSWFFSM and the single-stator WFFSM are similar, the torque per volume for the DSWFFSM is shown to be significantly exceptional. The torque ripple in the DSWFFSM is also smaller, but the efficiency is slightly lower than the single-stator WFFSM. The DSWFFSM design, which is shown to be comparable to PM-based topologies in terms of power density, highlights a low-cost, sustainable, clean energy generator topology. Full article

Neodymium-based permanent magnets are strategic materials for the global energy transition, supporting technologies such as wind turbines and electric motors. However, the concentration of supply and the environmental impacts of rare-earth mining raise concerns about supply-chain security and technological dependence. This study analyzed the international scientific output on neodymium within the energy transition framework, identifying temporal trends, research areas, influential authors, and the geographic distribution of knowledge. The PROKNOW-C method was applied to the Scopus database, covering the period from 2004 to 2024. After filtering and standardization steps, 1384 documents were analyzed using VOSviewer to map networks of co-authorship, co-citation, and keyword co-occurrence. The results indicated a growth in publications after 2015, coinciding with intensifying debates on sustainability and technological innovation. These publications are concentrated around three main themes: energy efficiency in motors and technological advancements in wind turbine generators, circular economy strategies, and the development of alternative materials. Scientific output is led by China, the United States, and Japan. Ultimately, this mapping reveals that while the electromechanical application of neodymium is a consolidated field, there is an urgent need to foster research and public policies focused on recycling technologies to mitigate supply-chain vulnerabilities and ensure the material security of the global energy transition. Full article

Archaeomagnetic studies provide crucial information on the spatial and temporal evolution of the geomagnetic field as recorded in rocks and archeological artifacts, offering insights into both Earth’s magnetic evolution and past geological and human activities. Measurements of the direction, intensity, and relative variations in the Earth’s Magnetic Field (EMF) are performed using sensitive magnetometers. Among these, induction magnetometers exploit Faraday’s law of electromagnetic induction to measure magnetic fields with high precision. In this work, we present a comparison between two different configurations of Helmholtz-based induction magnetometers carried out through the analysis of the magnetic field distribution obtained through analytical simulations. The study examines both the uniformity and intensity of the magnetic fields produced by each configuration, highlighting the influence of coil geometry on field homogeneity and sensitivity. The results reveal differences between the two configurations, providing important insights for optimizing magnetometer design, improving measurement accuracy, and facilitating analytical procedures in archaeomagnetic research. Full article

Rare-earth permanent magnet synchronous motors (PMSMs) are commonly used in new energy vehicles, wind power generation, and other relevant fields due to their advantages of small size and high power density. The operation of this type of motor depends on a rare-earth permanent magnet. However, the compatibility between the permanent magnet and the motor under different motor operating conditions is unclear, which is unfavorable for the subsequent selection of motor magnets. In this study, the effects of the permanent magnet on motor performance in different operational environments were analyzed. Three different magnets, namely, N-52M, N-48SH, and SmCo-28H, were selected. Two types of operational conditions were selected: the motor temperature and input current. The load torque, the magnet’s demagnetization behavior, and the magnet’s cost-effectiveness were discussed. The results indicate that the N-52M magnet was suitable for a low temperature and low input current due to its high remanence. However, the SmCo-28H magnet should be used at high temperatures and input currents due to its superior anti-demagnetization properties. The results obtained in this study will enable comparison of the effects of different permanent magnet materials on the motor, thereby guiding the subsequent design of PMSMs. Full article

An IoT-based technique is suggested for detecting single-phase earth faults (SEFs) in 6–35 kV cable networks with an isolated neutral. Unlike existing methods based on measuring zero-sequence currents with traditional current transformers, the suggested technique uses a passive magnetically controlled contact (reed switch) placed in the magnetic field of a cable. This enables recording fault currents of 0.5–2.0 A without external power supply and ensures galvanic isolation. The novelty of this technique is the combination of a reed switch current sensor with an IoT platform: instantaneous values of current are measured by the duration of the closed state of the contacts, then the data are transmitted via a radio channel (LoRa 433 MHz, LoRaWAN, or NB-IoT) to a cloud-based SCADA/EMS system for remote monitoring. The amplitude of the current is calculated from the pickup and resetting currents, as well as the duration of the closed state of the contacts; no high-frequency ADC is required. During experimental tests of a prototype with a KEM-5 reed switch and a TZL-10 current transformer, the difference between the calculated and actual protection operation current was no more than 10–5%. Oscillograms confirmed the correct operation of the device when starting, under load, and during an artificial SEF with a current of 1.6 A. The device response time is a fraction of the industrial frequency period, which significantly reduces the emergency mode duration. The suggested system enables decreasing the system average interruption duration index (SAIDI) and the system average interruption frequency index (SAIFI) by selectively disconnecting a damaged section and preventing cascading faults. The use of two independent channels (current transformer and reed switch) increases the reliability of SEF detection and reduces the risk of false operation. Thus, the developed IoT-based technique improves the reliability, safety, and cost-effectiveness of cable network operation. Full article