Magnetic Properties Of Materials Research Articles

Supercritical CO2-Induced Chemical Pressure on BaZrO3 for Room-Temperature Ferromagnetism.

The modulation of intrinsic magnetic properties of materials is of great importance for the exploration of new materials in the fields of information storage and spintronics. Herein, room-temperature ferromagnetic properties in BaZrO3 are successfully induced using supercritical CO2. The highest saturation magnetization intensity of BaZrO3 is observed at 16MPa, with a value of 0.08189 emu g-1. It is noteworthy that this technique is observed to modulate the ferromagnetic properties of the material by converting the external physical pressure into the chemical pressure within the material through the intercalation and de-intercalation of CO2 molecules. This result gives us a new understanding of the modification mechanism of SC-CO2, which is important for material modification.

Effect of Hubbard U-corrections on the electronic and magnetic properties of 2D materials: a high-throughput study

We conduct a systematic investigation of the role of Hubbard U corrections in electronic structure calculations of two-dimensional (2D) materials containing 3d transition metals. Specifically, we use density functional theory (DFT) with the PBE and PBE+U approximations to calculate the crystal structure, band gaps, and magnetic parameters of 638 monolayers. Based on a comprehensive comparison to experiments we first establish that the inclusion of the U correction worsens the accuracy for the lattice constants. Consequently, PBE structures are used for subsequent property evaluations. The band gaps show a significant dependence on U. In particular, for 134 (21%) of the materials the U parameter induces a metal-to-insulator transition. For the magnetic materials we calculate the magnetic moment, magnetic exchange coupling, and magnetic anisotropy parameters. In contrast to the band gaps, the size of the magnetic moments shows only weak dependence on U. Both the exchange energies and magnetic anisotropy parameters are systematically reduced by the U correction. On this basis we conclude that the Hubbard U correction will lead to lower predicted Curie temperatures in 2D materials. All the calculated properties are available in the Computational 2D Materials Database (C2DB).

A Compendium of Magnetic Nanoparticle Essentials: A Comprehensive Guide for Beginners and Experts.

Magnetic nanoparticles (MNPs) are advanced materials that combine the unique properties of magnetic materials and nanoscale dimensions, enabling a wide range of applications in biomedicine, environmental science, and information technology. This review provides a comprehensive yet accessible introduction to the fundamental principles, characterization techniques, and diverse applications of MNPs, with a focus on their nanoscale magnetic properties, such as superparamagnetism, single-domain behavior, and surface effects. It also delves into their classification and the critical role of parameters like magnetic anisotropy and blocking temperature. Emphasis is placed on routine characterization methods, including X-ray diffraction, electron microscopy, and magnetometry, as well as advanced concepts like magnetic hyperthermia and self-regulated heating. Designed for newcomers and experts alike, this review serves as both an educational guide and a quick-reference resource, ensuring clarity while maintaining scientific rigor.

High-Coercivity Ferrimagnet Co₂FeO₂BO₃: XMCD Insights into Charge-Ordering and Cation Distribution

The multi-sublattice ferrimagnet Co2FeO2BO3, a prominent example of lanthanide-free magnets, was the subject of element-selective studies using X-ray magnetic circular dichroism (XMCD) observations at the L- and K- X-ray absorption edges. Research findings indicate that the distinct magnetic characteristics of Co2FeO2BO3, namely its remarkable high coercivity (which surpasses 7 Tesla at low temperatures), originate from an atypical arrangement of magnetic ions in the crystal structure (sp.gr. Pbam). The antiferromagnetic nature of the Co2+-O-Fe3+ exchange interaction was confirmed by identifying the spin and orbital contributions to the total magnetization from Co (mL = 0.27 ± 0.1 μB/ion and meffS = 0.53 ± 0.1 μB/ion) and Fe (mL = 0.05 ± 0.1 μB/ion and meffS = 0.80 ± 0.1 μB/ion) ions through element-selective XMCD analysis. Additionally, the research explicitly revealed that the strong magnetic anisotropy is a result of the significant unquenched orbital magnetic moment of Co, a feature that is also present in the related compound Co3O2BO3. A complex magnetic structure in Co2FeO2BO3, with infinite Co²⁺O6 layers in the bc-plane and strong antiferromagnetic coupling through Fe3⁺ ions, is suggested by element-selective hysteresis data, which revealed that Co²⁺ ions contribute both antiferromagnetic and ferromagnetic components to the total magnetization. The findings underline the suitability of Co2FeO2BO3 for applications in extreme environments, such as low temperatures and high magnetic fields, where its unique magnetic topology and anisotropy can be harnessed for advanced technologies, including materials for space exploration and quantum devices. This XMCD study opens the door to the production of novel high-coercivity, lanthanide-free magnetic materials by showing that targeted substitution at specific crystallographic sites can significantly enhance the magnetic properties of such materials.

DFT + U study of structural, electronic, optical and magnetic properties of LiFePO4 Cathode materials for Lithium-Ion batteries

Abstract In this study, we have investigated the structural, electronic, optical, and magnetic properties of LiFePO4 (LFP), which is a prominent cathode material for lithium-ion batteries (LIBs). In order to analyse the properties of LFP, we have carried out the calculations using Density Functional Theory (DFT) combined with the Hubbard (U) correction (i.e., DFT + U), as implemented in the quantum-espresso (QE) code. We performed the structural optimization and found that LFP has a stable olivine structure with equilibrium parameters of a = 4.64 Å, b = 5.98 Å, and c = 10.34 Å. It is shown that LFP has a direct band gap value of 3.82 eV, which is very close to experiment values of 3.6-4.0 eV. The projected density of states (PDOS) of the LFP closely matches with experimental reports of the electronic structure of the material, where the Fe 3d states form tight bands above the O 2p band. The analysis of optical properties shows a significant absorption property in the visible spectrum, reflecting its additional potential for photoactive application. We have also examined the magnetic properties, which reveal that LFP exhibits antiferromagnetic ordering, which plays a critical role in the stability of the material during lithium cycling. The investigated properties of LFP in this work, thus, highlight its viability as an effective cathode material for the next-generation battery technologies with a multifaced applications.

Control of Dielectric, Mechanical, and Thermal Properties of a Polymer Composite Based on ABS Using CoB Nanoparticles.

This article is devoted to the development of a new method for the synthesis of magnetic cobalt boride nanoparticles using a low-energy approach. The obtained nanoparticles were used to create composite materials based on industrial thermoplastic ABS. The effect of different concentrations of nanoparticles on the physical, mechanical, magnetic, and dielectric properties of composite materials was studied. It was proven that by varying the concentration of nanoparticles in the ABS composite, it is possible to control the glass transition temperature from 107.5 to 112 °C. The resulting composites demonstrated superparamagnetic behavior, which changed linearly. The permittivity of the composite remained close to that of pure ABS, but a shift in the maximum permittivity to the low-frequency region was observed with an increase in the content of nanoparticles. Thus, a method for controlling the mechanical, magnetic, and dielectric properties of a composite material has been developed, which makes it possible to use routine ABS in a wider range of applications, including electrical devices.

Impact of the STFT Window Size on Classification of Grain-Oriented Electrical Steels from Barkhausen Noise Time–Frequency Spectrograms via Deep CNNs

The Magnetic Barkhausen Noise (MBN) is a non-destructive testing method, which, due to its high sensitivity to changes in the microstructure of the material, is increasingly being applied with success as a tool for evaluation of magnetic material state and properties. However, it is no less difficult to analyze the measurement signals and their correct interpretation due to the complex, non-deterministic and stochastic nature of the Barkhausen phenomenon. Depending on the material to be examined, a signal with different characteristics can be observed. Frequently, a signal with multi-phase Barkhausen activity characteristics is obtained, like in the case of grain-oriented electrical steels. Due to the increased computational capabilities of computers, more and more advanced signal analysis methods are being used and artificial intelligence is being involved as well. Recently, the time–frequency (TF) approach for MBN signal analysis was introduced and discussed in several papers, where short-time Fourier Transform (STFT) found frequent application with promising results. Due to the automation of the search for diagnostic patterns, the stage of selecting transformation parameters becomes extremely important in the process of preparing training data for evaluation algorithms. This paper investigates the influence of the STFT computational window size on the material state evaluation results obtained using convolutional neural network (CNN). The studies were performed for MBN signals obtained from grain-oriented electrical steel with anisotropic properties. The carried out work made it possible to draw connections on the importance of the choice of the window during the implementation of CNN network training.

Research on magnetic force of magnetic seal in aero-engine

Aiming at the magnetic seal in an aero-engine accessory, the range of magnetic force required for the normal operation of the magnetic seal is analyzed. The finite element analysis method based on the Maxwell stress tensor method is used to calculate the magnetic force between the dynamic ring and the magnetic static ring in the magnetic sealing system. The magnetic force under different magnetization modes and gaps is tested by the magnetic measuring test bench, which verifies the correctness of the magnetic calculation method. The effects of permanent magnet material, permanent magnet magnetization direction, magnetic seal structural parameters, and working conditions on the magnetic force between the dynamic ring/magnetic static ring in the magnetic seal are analyzed. Under the same structure, the magnetic force of NeFeB35, SmCo28, Alnico5, and Ferrite as magnetic static rings is compared. The results show that NdFeB35 has the largest magnetic force, SmCo28 is second, Alnico5 and Ferrite are relatively small, and their magnetic forces are about 1/4 to 1/5 of the first two materials. When the rotor or the casing is moving axially, NeFeB35 and SmCo28 materials with large magnetic force should be selected to meet the normal working requirements. Under the same material, the magnetic forces of axial, radial, and radiative magnetization modes are compared. the ratio of magnetic force under axial, radiative, and radial magnetization is about 2.3:1.1:1. If NeFeB35 and SmCo28 materials are axially magnetized, their magnetic forces will exceed the allowable range, which will increase the seal wear. The increase in the inner diameter of the dynamic ring and the gap between the dynamic ring and the magnetic static ring causes a decrease in the magnetic force. The increase in temperature affects the magnetic properties of permanent magnetic material, which leads to the decline of magnetic force between the dynamic ring and the magnetic static ring. The increase in rotor speed leads to the acceleration of the fluctuation frequency of the magnetic force. Still, the maximum and minimum values of the magnetic force under different speeds remain unchanged, and the maximum fluctuation rate is less than 3%. According to the analysis results, the fitting formula of magnetic force calculation is presented by the orthogonal test and the least squares method.

Investigation of certain physical properties of Co2MnGe Heusler: DFT calculation and Monte Carlo simulation

In this work, we have used the first-principles method based on Density Functional Theory (DFT) to study the electronic structure, density of states, band structure, and exchange couplings of the Heusler compound Co₂MnGe. This material's magnetic properties were investigated through the use of Monte Carlo simulations (MCS) in the framework of a three-dimensional Ising model. In particular, we evaluated the magnetization, magnetic susceptibility, specific heat, and Binder cumulant, and calculated some critical exponents of the system. The results showed that the Heusler compound Co₂MnGe exhibits a semi-metallic behavior and undergoes a transition from the ferromagnetic to the paramagnetic phase at a critical temperature Tc ≈ 990 K, in good agreement with the experimental data. The values of the calculated critical exponents are very similar to those known for the three-dimensional Ising model: α ≈ 0.1191, β ≈ 0.3188, γ ≈ 1.2526, and ν ≈ 0.5526, verifying the universal behavior of the studied system.

The Estimation of Power Losses in Composite Cores Excited by Harmonic Flux Density Waveforms

This paper presents a study of the empirical approach to the estimation of power losses in composite cores excited by harmonic flux density waveforms. Nowadays, magnetic cores operating in power electronic devices are excited by distorted (e.g., harmonic) flux density waveforms. Magnetic material properties are mostly determined for sinusoidal waveforms of the magnetic flux density. However, these properties can vary significantly in the case of harmonic excitations, which affects the devices’ efficiency. The effect of harmonic flux density waveform parameters (amplitude ratio and phase angle) on the level of power losses in soft magnetic composites is analyzed. A simple, empirical model of harmonic losses based on standardized measurements, i.e., carried out for sinusoidal flux density waveforms, is modified and validated. It is revealed that the empirical approach to estimating harmonic losses can be applied to magnetic composites with satisfactory modelling results.

Role of substitution Zr-site on the electronic structure and magnetic properties of BaTiO3 materials: A first principles calculation

In this study, we employ density functional theory calculations to investigate the electronic band structures, density of states, and magnetic properties of pure BaTiO3 and Zr-doped BaTiO3 compounds. The intrinsic BaTiO3 compound exhibits an indirect band gap of 1.80 eV, which is larger than the range of 1.61–1.71 eV observed for Zr-doped BaTiO3. By systematically exploring the Zr substitution at different Ti sites, we analyze the impact of Zr doping on the electronic structure of BaTiO3 materials. The introduction of Zr doping induces significant modifications in the band structure and density of states, resulting in the emergence of new energy levels within the band gap. These findings enhance the understanding of the electronic properties of BaTiO3 and Zr-doped BaTiO3 materials, paving the way for potential applications in electronic and optical devices.

Strain-tunable electronic and magnetic properties of two-dimensional CrSBr material

Abstract Two-dimensional (2D) materials, particularly those with intrinsic magnetism, hold promise for next-generation spintronic devices due to their unique electronic and magnetic properties. This study investigates the impact of in-plane uniaxial and biaxial strain on the properties of monolayer CrSBr using density functional theory (DFT) and Monte Carlo (MC) simulations. We demonstrate that strain engineering can effectively modulate the electronic band structure and Curie temperature (Tc) of the CrSBr monolayer. Under uniaxial strains, transitions from indirect to direct bandgaps are observed, enhancing semiconductor characteristics. Importantly, compressive strain along the y-direction significantly increases Tc, potentially approaching room temperature. These findings highlight the role of strain manipulation in tailoring the functionality of 2D magnetic materials, crucial for advancing spintronics and nanoelectronic applications.

Influence of magnetic interaction on four-peak GMI profile in FINEMET/Fe35Ni65 composite ribbons

The study of magnetic interactions is crucial in understanding magnetic materials, where both exchange coupling and dipole interactions significantly affect the magnetic properties of composite materials. Separating and utilizing these two types of interactions have consistently been a research focus. In this study, FINEMET/Fe35Ni65 composite ribbons with varying coating thicknesses were fabricated using magnetron sputtering. Notably, obvious four-peak giant magnetoimpedance profiles can be observed as the Fe35Ni65 film thickness varied from 10 to 50 nm. Additionally, the manifestation of the four-peak profile was attributed to the variation in the magnetic properties in the FINEMET ribbon induced by exchange coupling and dipole interaction. This analysis is crucial for advancing our understanding of the underlying physical mechanisms of magnetic interactions in composite ribbons.

Adsorption removal of copper(II) from water by zero valent iron loaded dendritic mesoporous silica

The object of research is synthesized dendritic mesoporous nanoscale silica (DMSN) modified with zero-valent iron (Fe0@DMSN). This material exhibits a high adsorption capacity for heavy metal ions, in particular copper, whose increased content in the aquatic environment poses a threat to living organisms. In this regard, the main physicochemical features of the removal of copper cations from the aqueous medium using the obtained sample were investigated. The morphology of the obtained dendritic silicas was studied by electron microscopy and the presence of a layer of zero-valent iron was confirmed by X-ray diffraction analysis and infrared spectroscopy. The parameters of the porous structure of the synthesized materials were determined. It was found that after modification of mesoporous silica with particles of zero-valent iron, the value of its specific surface area decreased from 504 m2/g to 312 m2/g. This may be due to the formation of a Fe0 layer not only on their surface but also in the channels of the inorganic matrix, which has a unique dendritic structure characteristic of this type of particles. At the same time, the number of active centers increases due to the enrichment of the silica surface with functional modifier groups that show a high affinity for metal cations. The adsorption capacity of Fe0@DMSN towards Cu2+ ions has been studied and it has been shown that the maximum adsorption value is 39.8 mg/g, which is significantly higher than that of the initial synthesized DMSN sample (0.7 mg/g). The experimental data obtained indicate that the obtained sorption material based on dendritic mesoporous silica nanoparticles with a layer of reactive zero-valent iron can be used for the purification of water contaminated with metal ions. In addition, the magnetic properties of such materials, known and proven by various scientists, will make it easy to separate the solid phase in the processes of sorption water purification using magnetic separation.

New Magnetic Materials and Technologies: Experiment and Theory

This article presents a brief review of works devoted to the latest research by a number of Russian groups involved in the development, creation, and study of the physical properties of new magnetic materials and the phenomena observed in them. These studies are of both great fundamental and practical interest for various fields of science, engineering, and new technologies.

Time-resolved x-ray imaging of nanoscale spin-wave dynamics at multi-GHz frequencies using low-alpha synchrotron operation

Time-resolved x-ray microscopy is used in a low-alpha synchrotron operation mode to image spin dynamics at an unprecedented combination of temporal and spatial resolution. Thereby, nanoscale spin waves with wavelengths down to 70 nm and frequencies up to 30 GHz are directly observed in ferromagnetic thin film microelements with spin vortex ground states. In an antiparallel ferromagnetic bilayer system, we detect the propagation of both optic and acoustic modes, the latter exhibiting even a strong non-reciprocity. In single-layer systems, quasi-uniform spin waves are observed together with modes of higher order (up to the 4th order), bearing precessional nodes over the thickness of the film. Furthermore, the effects of magnetic material properties, film thickness, and magnetic fields on the spin-wave spectrum are determined experimentally. Our experimental results are consistent with numerical calculations from a micromagnetic theory even on these so-far unexplored time- and length scales.

High anisotropy 2D large-size iron-based coral for C-band ultra-wide microwave absorption

Lightweight microwave-absorbing (MA) materials with broadband absorption in the C-band remain challenging to date. Recent studies have shown that promoting anisotropy in materials is expected to break the Snoek limit and enhance the absorption performance of magnetic materials in the C-band. In this paper, two-dimensional (2D) large-size coral-like iron-based composites (LCIC) were prepared using an NH4NO3-assisted blow molding separation strategy. The special structure with large shape anisotropy realizes a wide and strong natural magnetic resonance, leading to strong magnetic loss. The enhanced natural resonance effectively broadens the effective absorption bandwidth (EAB) of the LCIC in the C-band. The minimum reflection loss (RLmin) of LCIC is −41.64 dB, and the EAB is 5.42 GHz (3.83–9.25 GHz), covering the entire C-band. Strong natural resonance is necessary to improve the dissipation of magnetic losses in low-frequency electromagnetic waves. This work explores the important role of size effect in enhancing the C-band absorption properties of magnetic materials. It provides a feasible reference for the preparation of C-band broadband, strongly absorbing MA materials.

Imaging atomic-scale magnetism with energy-filtered differential phase contrast method

We propose differential phase contrast (DPC) imaging using energy-filtered electrons to image the magnetic properties of materials at the atomic scale. Compared to DPC measurements with elastic electrons, our simulations predict about two orders of magnitude higher relative magnetic signal intensities and sensitivity to all three vector components of magnetization. Published by the American Physical Society 2024

The effect of Mn doping on the electrical and magnetic properties of Cr2Te3 thin films

Mn doped Cr2-xMnxTe3 thin films were prepared by molecular beam epitaxy technology. The effect of Mn doping concentration on the structural, morphological, electrical and magnetic performance of Cr2Te3 thin films were detailed analyzed. By varying the beam current of the Mn source, it is found that Mn can be doped into the Cr2Te3 thin film when the Mn source temperature is lower than 700 ℃, while the Mn tends to bind with Te as MnTe crystal for Mn source temperature higher than 700 ℃. Cr2-xMnxTe3 films all exhibt strong ferromagnetism with a Curie temperature of around 175 K. The magnetization of the films decreases with increasing Mn doping concentration. A notable negative magnetoresistance effect is observed with the highest MR ratio about −60 % in the vicinity of the Curie temperature. A clear topological Hall signal was observed in the sample with a Mn source temperature of 700 ℃ at low temperature (2 K). These results imply that the electrical and magnetic properties of Cr2Te3 materials can be effectively controlled by doping to meet the practical needs of different fields.

Corrosion resistance of modified amorphous cobalt alloys

Amorphous metal alloys (AMА) based on Co have high corrosion resistance, which exceeds the durability of samples based on Fe, and also have the properties of soft magnetic materials. Therefore, new cobalt amorphous tape alloys can be used in medicine, in particular, as implants. An important indicator of AMC is the temperature and time interval of their use without a change in properties, that is, their level of stability, which depends on the chemical composition of the alloys and, certainly, on the conditions of production and use. At the same time, the properties of cobalt-based amorphous alloys can be changed by modification in various ways, in particular, by exposure to alternating magnetic fields. In this regard, electrochemical and structural studies of a number of AMAs based on Co are expedient: Co73,6Fe3,2Mn3,2Si5B15, Co73,6(Fe,Ni,Mo,Mn)5,7(Si0,2B0,8)21 and Co75,5Fe4,6Si6B16,7 original and modified in 0.9 % NaCl aqueous solution. The electrochemical characteristics of strip amorphous metal alloys Co73,6Fe3,2Mn3,2Si5B15, Co73,6(Fe,Ni,Mo,Mn)5,7(Si0,2B0,8)21 and Co75,5Fe4,6Si6B16,7 in 0 .9 % NaCl aqueous solution. For the first time, the influence of preliminary exposure in an alternating magnetic field for (0.5–3.0) h on the corrosion resistance of the amorphous Co73,6Fe3,2Mn3,2Si5B15 alloy was evaluated. The activation of the contact surface and the passivation of the outer surface of the alloy tape were established depending on the exposure, which is reflected by the corresponding change in the electrochemical parameters in a 0.9 % NaCl aqueous solution. Comparative comprehensive study of Co73,6Fe3,2Mn3,2Si5B15, Co73,6(Fe,Ni,Mo,Mn)5,7(Si0,2B0,8)21 and Co75,5Fe4,6Si6B16,7 alloys in 0.9 % aqueous solution NaCl showed that after the action of an alternating magnetic field, the difference in the final potential values of both the contact and outer surfaces of the ribbons of amorphous alloys is leveled. Research results are useful for manufacturers and consumers of amorphous materials.