Magnetic Properties Research Articles

Comparison of a quasi Newton method using Broyden’s update formula and an adjoint method for determining local magnetic material properties of electrical steel sheets

Purpose Performing accurate numerical simulations of electrical drives, the precise knowledge of the local magnetic material properties is of utmost importance. Due to the various manufacturing steps, e.g. heat treatment or cutting techniques, the magnetic material properties can strongly vary locally, and the assumption of homogenized global material parameters is no longer feasible. This paper aims to present the general methodology and two different solution strategies for determining the local magnetic material properties using reference and simulation data. Design/methodology/approach The general methodology combines methods based on measurement, numerical simulation and solving an inverse problem. Therefore, a sensor-actuator system is used to characterize electrical steel sheets locally. Based on the measurement data and results from the finite element simulation, the inverse problem is solved with two different solution strategies. The first one is a quasi Newton method (QNM) using Broyden's update formula to approximate the Jacobian and the second is an adjoint method. For comparison of both methods regarding convergence and efficiency, an artificial example with a linear material model is considered. Findings The QNM and the adjoint method show similar convergence behavior for two different cutting-edge effects. Furthermore, considering a priori information improved the convergence rate. However, no impact on the stability and the remaining error is observed. Originality/value The presented methodology enables a fast and simple determination of the local magnetic material properties of electrical steel sheets without the need for a large number of samples or special preparation procedures.

Liquid-Metal-Based Spin-Coating Exfoliation for Atomically Thin Metal Oxide Synthesis.

Two-dimensional (2D) semiconductors possess exceptional electronic, optical, and magnetic properties, making them highly desirable for widespread applications. However, conventional mechanical exfoliation and epitaxial growth methods are insufficient in meeting the demand for atomically thin films covering large areas while maintaining high quality. Herein, leveraging liquid metal oxidation reaction, we propose a motorized spin-coating exfoliation strategy to efficiently produce large-area 2D metal oxide (2DMO) semiconductors with high crystallinity, atomically thin thickness, and flat surfaces on diverse substrates. Moreover, we realized a 2D gallium oxide-based deep ultraviolet solar-blind photodetector featuring a metal-semiconductor-metal structure, showcasing high responsivity (8.24 A W-1) at 254 nm and excellent sensitivity (4.3 × 1012 cm Hz1/2 W-1). This novel liquid-metal-based spin-coating exfoliation strategy offers great potential for synthesizing atomically thin 2D semiconductors, opening new avenues for future functional electronic and optical applications.

Experimental and Theoretical Insights on the Structural, Electronic, and Magnetic Properties of the Quaternary Selenides EuPrCuSe3 and EuNdCuSe3.

Magnetic semiconductors EuPrCuSe3 and EuNdCuSe3 were obtained by using the halide flux method. Their crystal structures and magnetic properties were studied and discussed. Optical properties of the obtained selenides were studied by the means of diffuse reflectance spectroscopy, which revealed the values of 1.92/1.97 and 0.90/0.94 eV for the direct and indirect band gaps of Ln = Nd/Pr, respectively. The structural, electronic, and magnetic properties of the obtained compounds were additionally studied with spin-polarized density functional theory calculations, wherein both systems were found to be two new examples of semiconducting quaternary selenides with disperse conduction bands of Nd/Pr 5d character. The modeling showed that various magnetic orderings in the systems have subtle influences on the alignments/overlaps between the Se/Cu, Eu, and Pr/Nd bands, and that the spin-state energetics are very dependent upon the treatment of electron correlation, but a distinguishing feature in the case of ferromagnetic coupling is that the spin density on the Se atoms is maximized. Overall, the calculations are in good agreement with the experimental characterization of ferromagnetism in the bulk crystals, wherein the ferromagnetic transition occurs at temperatures of about 2.5 K for EuPrCuSe3 and about 3 K for EuNdCuSe3.

Strategic grain boundary diffusion process for high-performance Ce-containing sintered Nd-Fe-B magnets

Sintered Nd-Fe-B magnets are an important driver of green technology, and the grain boundary diffusion process (GBDP) has become the most economically efficient method to improve the overall magnetic properties of sintered Nd-Fe-B magnets. In the work, to further reduce the utilization cost of sintered Nd-Fe-B permanent magnets with high performance, the strategic GBDP was explored based on the demagnetization characteristics of Nd-Fe-B permanent magnet materials in motors. The peculiar fact about the process was that the diffusion source was deposited on a part of the c-plane, that is, the strategic selected area grain boundary diffusion process (S-SAGBDP). With the objective of addressing the edge demagnetization, the diffusion source was initially deposited only at the edges of the c-plane. Despite the overall magnetic properties and temperature coefficients of the diffused magnet were significantly enhanced, the serious deteriorations of squareness and surface magnetic field were particularly worrying. Consequently, the central area of the magnet was simultaneously strengthened. The squareness and demagnetization property of the magnet after S-SAGBDP were greatly improved, and the amount of heavy rare earths was reduced by 25%. The above work clearly illustrates the practical value of S-SAGBDP, which is helpful to develop the cost-effective and commercial-grade sintered Nd-Fe-B magnets.

Coercivity enhancement and microstructure optimization of Nd-Fe-Co-B magnets by Dy70Al10Cu20 grain boundary diffusion

The effect of grain boundary diffusion on the magnetic properties and microstructure of Nd-Fe-Co-B sintered magnets is investigated using Dy70Al10Cu20 alloy as the diffusion source. After the secondary annealing of the Nd-Fe-Co-B sintered magnet (Hcj = 7.94 kOe), its coercivity is substantially increased to 13.10 kOe. Following post-diffusion annealing, the coercivity of the sintered magnet significantly increased to 20.86 kOe. Microstructure analysis revealed that after the second annealing, the main phase grains in the magnet were connected but lacked thin intergranular phases. The distribution of Co was uneven, with an abundance of soft magnetic phases rich in Co, which was not conducive to improving coercivity. After diffusion, Dy formed a shell structure with high magnetic crystal anisotropy on the outer side of the main phase grains, leading to a significant increase in coercivity. Al and Cu entered the interior of the magnet, reducing the melting point of the grain boundary phase and promoting the uniform distribution of Co through the flow of the liquid phase. A large amount of thin continuous intergranular phase is generated inside the magnet, which helps reduce the exchange coupling between hard magnetic grains. The experimental results indicate that the Dy-Al-Cu alloy can effectively enhance the grain boundary structure of Nd-Fe-Co-B magnets, reduce the abundance of Co-rich phases, and improve the coercivity of the magnet.

Fabrication and characterization of rubidium ferrites by the solution‐based combustion method using diverse organic fuels

Fabrication and characterization of rubidium ferrites by the solution‐based combustion method using diverse organic fuels

Optical control and coherent coupling of spin diffusive modes in thermal gases

Quantum science and technology devices exploiting collective spins in thermal gases are extremely appealing due to their simplicity and robustness. This comes at the cost of dealing with the random thermal motion of the atoms which is usually an uncontrolled source of decoherence and noise. There are however conditions, for example, when diffusing in a buffer gas, where thermal atoms can occupy a discrete set of stable spatial modes. Diffusive modes can be extended or localized, have different magnetic properties depending on boundary conditions, and can react differently to external perturbations. Here, we selectively excite, manipulate, and interrogate the longest-lived of these modes by using laser light. In particular, we identify the conditions for the generation of modes that are exceptionally resilient to detrimental effects such as light induced frequency shifts and power-broadening, which are often the dominant sources of systematic errors in atomic magnetometers and comagnetometers. Moreover, we show that the presence of spatial inhomogeneities in the pump introduces a coupling that leads to a coherent exchange of excitation between the two longest-lived modes. Our results demonstrate that systematic engineering of the multi-mode nature of diffusive gases has great potential for improving the performance of quantum sensors based on alkali-metal thermal vapors, and opens new perspectives for quantum information applications. Published by the American Physical Society 2024

Effects of 1:5H-type Cu-rich phase around grain boundary on cell boundary phase and squareness of the demagnetization curve in sintered Sm2Co17-type magnets

The unique cellular structure of Sm2Co17-type magnets is responsible for their outstanding magnetic properties. However, the cell boundary phase around grain boundaries is few, and cannot form a complete cellular structure. This study explores the microstructure and microchemistry of the grain interiors and grain boundary regions in both the solid solution precursor and the final magnet. The Cu-rich phase precipitates around grain boundaries in the solid solution precursor, and it remains present in the final magnet. The Cu-rich phase is not present as a standalone grain boundary phase, rather, it possesses a hexagonal CaCu5-type crystal structure and demonstrates a coherent orientation relationship with the surrounding matrix. The Cu-rich phase inhibits cellular structure formation nearby, while boosting Cu content in the cell boundary phase at the grain boundary regions in the final magnet. The formation of a Cu-rich phase around the grain boundary increases the heterogeneity of the domain wall pinning field in the final magnet, becoming an unfavorable factor for the improvement of the squareness of the demagnetization curve. These discoveries enhance our comprehension of the precipitated phase surrounding the grain boundary and its impact on the cellular structure and magnetic characteristics of the magnet.

Half-metal Mn2GeI2 monolayer with high Curie temperature and large perpendicular magnetic anisotropy

Two-dimensional (2D) intrinsic ferromagnetic (FM) materials with high Curie temperatures (Tc), large perpendicular magnetic anisotropy (PMA), and large spin polarization are desirable for atomically thin spintronic devices. Herein, we propose a 2D intrinsic FM material Mn2GeI2 monolayer with thermodynamical stability and outstanding FM properties using first-principles calculations. Our calculations show that Mn2GeI2 monolayer is a half-metal with a spin gap of 1.76 eV, which ensures 100% spin polarization ratio at the Fermi level. Importantly, Mn2GeI2 monolayer has a large PMA energy of 2.90 meV and a high Tc of 648 K, ideal for practical applications at room temperature. Further in-depth investigation of microscopic coupling in the Mn2GeI2 monolayer reveals that the robust ferromagnetism mainly resulted from the synthetic effect of Ruderman–Kittel–Kasuya–Yosida exchange interaction between the Mn ion layers and superexchange interaction within the Mn ion layers. Our results give insights into the structure and electronic and magnetic properties of Mn2GeI2 monolayer and provide a promising candidate for 2D spintronic devices.

Unveiling the Low-Lying Spin States of [Fe3S4] Clusters via the Extended Broken-Symmetry Method.

Photosynthetic water splitting, when synergized with hydrogen production catalyzed by hydrogenases, emerges as a promising avenue for clean and renewable energy. However, theoretical calculations have faced challenges in elucidating the low-lying spin states of iron-sulfur clusters, which are integral components of hydrogenases. To address this challenge, we employ the Extended Broken-Symmetry method for the computation of the cubane-[Fe3S4] cluster within the [FeNi] hydrogenase enzyme. This approach rectifies the error caused by spin contamination, allowing us to obtain the magnetic exchange coupling constant and the energy level of the low-lying state. We find that the Extended Broken-Symmetry method provides more accurate results for differences in bond length and the magnetic coupling constant. This accuracy assists in reconstructing the low-spin ground state force and determining the geometric structure of the ground state. By utilizing the Extended Broken-Symmetry method, we further highlight the significance of the geometric arrangement of metal centers in the cluster's properties and gain deeper insights into the magnetic properties of transition metal iron-sulfur clusters at the reaction centers of hydrogenases. This research illuminates the untapped potential of hydrogenases and their promising role in the future of photosynthesis and sustainable energy production.

Strong magnetodielectric effect in Bi(La)Fe(Cr)O3 multiferroic nanomaterials

The Bi1-xLaxFe1-yCryO3 (x = 0.00, 0.06; y = 0.00, 0.03, 0.06, 0.09, 0.12) nanomaterials have been synthesized using the simple solvo-thermal technique. The Rietveld refinement of XRD analysis using FullProf Software confirms that all synthesized materials follow rhombohedral perovskite crystal structure of R3C space group. The dielectric and ac conductivity data are analyzed to understand the role of grain and grain boundary contributions. The enhancement of magnetic properties has been observed from SQUID measurement for the co-doped samples at room temperature. Also, a significant improvement in polarization has been observed for the doped nanocompounds from the ferroelectric hysteresis loop. The magneto-dielectric study reveals a large improvement in our co-doped BFO nanomaterials and the value is nearly three times of those reported earlier. The calculated energy storage efficiency for the co-doped samples are found to have as high as 51 %. The sample with x = 0.06 and y = 0.09 with a magneto dielectric coefficient of around 30 % and energy storage efficiency of 35 % is the most suitable for both spintronic and energy storage devices.

Turning Ultra-Low Coercivity and Ultra-High Temperature Stability Within 897 K via Continuous Crystal Ordering Fluctuations.

High-performance soft magnetic materials are important for energy conservation and emission reduction. One challenge is achieving a combination of reliable temperature stability, high resistivity, high Curie temperature, and high saturation magnetization in a single material, which often comes at the expense of intrinsic coercivity-a typical trade-off in the family of soft magnetic materials with homogeneous microstructures. Herein, a nanostructured FeCoNiSiAl complex concentrated alloy is developed through a hierarchical structure strategy. This alloy exhibits superior soft magnetic properties up to 897K, maintaining an ultra-low intrinsic coercivity (13.6 A m-1 at 297 K) over a wide temperature range, a high resistivity (138.08µΩcm-1 at 297K) and the saturation magnetization with only a 16.7% attenuation at 897 K. These unusual property combinations are attributed to the dual-magnetic-state nature with exchange softening due to continuous crystal ordering fluctuations at the atomic scale. By deliberately controlling the microstructure, the comprehensive performance of the alloy can be tuned and controlled. The research provides valuable guidance for the development of soft magnetic materials for high-temperature applications and expands the potential applications of related functional materials in the field of sustainable energy.

A copper- and amine-free sonogashira reaction catalyzed by a supported bis(oxime palladacycle) on magnetized SBA-15

The recently reported magnetic catalyst, Fe3O4@SBA-bis(oxime palladacycle), was incorporated in the Sonogashira reaction. The potential catalytic activity of the catalyst was evaluated by optimizing the reaction conditions. It was discovered that using dimethylsulfoxide (DMSO) as a solvent, a catalyst loading of 0.25 mol% palladium, Cs2CO3 as a base, and a reaction temperature of 120 °C resulted in the highest yields. The catalyst showed excellent activity with a wide range of aryl halides and aryl acetylenes in the Sonogashira reaction. The use of a low catalyst loading further highlighted its efficiency. Moreover, the catalyst demonstrated noteworthy reusability by consistently preserving its activity and stability through seven successive runs. The magnetic properties of the catalyst allowed for easy separation and recovery.

Magnetic Anisotropy and Relaxation in Four-Coordinate Cobalt(II) Single-Ion Magnets with a [CoIIO4] Core.

A mononuclear four-coordinate Co(II) complex with a [CoIIO4] core, namely, PPN[Li(MeOH)4][Co(L)2] (1) (PPN = bis(phosphoranediyl)iminium; H2L = perfluoropinacol), has been studied by X-ray crystallography, magnetic characterization, and theoretical calculations. This complex presents a severely distorted coordination geometry. The O-Co-O bite angle is 83.42°/83.65°, and the dihedral twist angle between the O-Co-O chelate planes is 55.6°. The structural distortion results in a large easy-axis magnetic anisotropy with D = -104(1) cm-1 and a transverse component with |E| = +4(2) cm-1. Alternating current (ac) susceptibility measurements demonstrate that 1 exhibits slow relaxation of magnetization at zero static field. However, the frequency-dependent out-of-phase (χ"M) susceptibilities of 1 at 0 Oe do not show a characteristic maximum. Upon the application of a dc field or the dilution with a diamagnetic Zn matrix, the quantum tunneling of magnetization (QTM) process can be successfully suppressed. Notably, after dilution with the Zn matrix, the obtained sample exhibits a structure different from that of the pristine complex. In this altered sample, the asymmetric unit does not contain the Li(MeOH)4+ cation, resulting in an O-Co-O bite angle of 86.05° and a dihedral twist angle of 75.84°, thereby leading to an approximate D2d symmetry. Although such differences are not desirable for magnetic studies, this study still gives some insights. Theoretical calculations reveal that the D parameter is governed by the O-Co-O bite angle, in line with our previous report for other tetrahedral Co(II) complex with a [CoIIN4] core. On the other hand, the rhombic component is found to increase as the dihedral angle deviates from 90°. These findings provide valuable guidelines for fine-tuning the magnetic properties of Co(II) complexes.

NiO/MnFe2O4 Nanocomposite Photoluminescence, Structural, Morphological, Magnetic, and Optical Properties: Photocatalytic Removal of Cresol Red under Visible Light Irradiation.

In this study, pure nickel oxide (NiO), manganese ferrite (MnFe2O4 or MFO), and binary nickel oxide/manganese ferrite (NiO/MFO1-4) nanocomposites (NCs) were synthesized using the Sol-Gel method. A comprehensive investigation into their photoluminescence, structural, morphological, magnetic, optical, and photocatalytic properties was conducted. Raman analysis, UV-Vis spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction techniques were used to characterize the materials. The synthesized samples exhibited superparamagnetic behavior, as revealed by our analysis of their magnetic properties. A lower recombination rate was shown by the photoluminescence analysis, which is helpful for raising photocatalytic activity. The photocatalytic activity was evaluated for the degradation of Cresol Red (CR) dye. 91.6% of CR dye was degraded by NiO/MFO-4 nanocomposite, and the NC dosage as well as solution pH affected the photocatalytic performance significantly. In four sequential photocatalytic cycles, the magnetically separable NCs were stable and recyclable. The enhanced photocatalytic activity and magnetic separability revealed the potential application of NiO/MFO-4 as an efficient photocatalyst for the removal of dyes from industrial wastewater under solar light irradiation.

Point Defects in Hexagonal SiP Monolayer: A Systematic Investigation on the Electronic and Magnetic Properties

AbstractIn this work, point defects are proposed to modify the electronic and magnetic properties of SiP monolayer. Pristine monolayer is a non‐magnetic semiconductor 2D material with energy gap of 1.52(2.21) eV as predicted by PBE(HSE06) functional. Single Si vacancy (), Si+P divacancy (), and substituting one P atom by one Si atom () magnetize significantly SiP monolayer. Herein, total magnetic moments between 1.00 and 2.00 are obtained . In contrast, no magnetism is induced by single P vacancy (), substituting one Si atom by one P atom (), and exchanging pair Si‐P positions (). Moreover, significant magnetization of SiP monolayer is also achieved by doping with single Li and Cu atoms ( and ), as well as pair of Li and Cu atoms ( and ). Total magnetic moments between 0.84 and 1.42 are obtained. Interestingly, the half‐metallicity is observed in and systems. When substituting P atom, F, Cl, and Br impurities reduce significantly the SiP monolayer bandgap, preserving its non‐magnetic nature. In contrast, a total magnetic moment of 1.26 is obtained by doping with I atom. Results presented herein may introduce the defected and doped SiP systems as prospective 2D candidates for spintronic and optoelectronic applications.

Computational exploration of Cs2LiMoX6 (X=Cl, I) halide double perovskites: Unveiling energy storage potentials

Density functional theory (DFT) simulations were conducted to investigate the physical characteristics of materials Cs2LiMoCl6 and Cs2LiMoI6. The magnetic and electronic features were examined using the Perdew, Burke, and Ernzerhof generalized-gradient approximation (PBE-GGA). Confirmation of the semiconductor behavior was attained through the spin-resolved density of states (DOS) and band structure (BS) plots. In this investigation, the computed band gap (Eg) values for Cs2LiMoI6 are identified as 0.96 eV in the spin-down channel and 1.76 eV in the spin-up channel. Likewise, for Cs2LiMoCl6, the Eg is determined to be 3.35 eV in the spin-down channel and 1.63 eV in the spin-up channel. From magnetic characteristics, the magnetic moments (μB) of 3.02436 μB and 3.00332 μB are calculated for Cs2LiMoCl6 and Cs2LiMoI6, respectively. The ferromagnetic (FM) nature is observed from the integral values of the magnetic moment. The Mo-4d-t2g orbitals play a pivotal role in determining the magnetic properties observed in perovskite materials. The study also explored optical properties, and the values of ε1(ω) at zero energy are approximately 4.84 and 3.20 for Cs2LiMoI6 and Cs2LiMoCl6, respectively. The maximum values of σ(ω) are observed to be 4631 (Ω cm)−1 and 3618 (Ω cm)−1 at 6.24 eV and 8 eV for Cs2LiMoI6 and Cs2LiMoCl6, respectively, signifying their suitability to the UV light region. Overall, these findings suggest the suitability of both materials for photovoltaics and other related applications.

The Effects of Si Substitution with C on the Amorphous Forming Ability, Thermal Stability, and Magnetic Properties of an FeSiBPC Amorphous Alloy

The Effects of Si Substitution with C on the Amorphous Forming Ability, Thermal Stability, and Magnetic Properties of an FeSiBPC Amorphous Alloy

Magnetic ground states and hyperfine interactions in YMnO[formula omitted] using density functional theory

This study employs the Local Density functional theory (DFT) and the DFT+U extension, to better describe the localized d-Mn states, and therefore analyze six magnetic configurations of the Mn ions in hexagonal manganite YMnO3. The respective study was complemented through hyperfine interaction calculations of different atomic configurations. Our focus is on six distinct magnetic configurations, complemented by thorough Hyperfine Interactions (HFI) calculations targeting the most plausible configuration. We find the P6’3 and P63 configurations are the most probable, aligning with previous research in the field. These configurations also show a strong correlation with experimental observations of magnetic moments, providing new insights into the magnetic ordering of YMnO3. Our results highlight the intricate relationship between magnetic moments and the lattice structure of YMnO3, offering valuable insights into the material’s magnetic properties.

Dielectric Properties and Magnetoelectric Effect of Bi7Fe3Ti3O21 Ceramic Material Doped with Gadolinium Ions

Dielectric Properties and Magnetoelectric Effect of Bi7Fe3Ti3O21 Ceramic Material Doped with Gadolinium Ions