Two-dimensional Magnetic Properties Research Articles

Static and dynamic magnetic properties in two-dimensional Lieb-like lattice

• Mixed spin Ising model was proposed to describe two-dimensional Lieb-like lattice. • Influence of the periodically oscillating magnetic field on the magnetism of two-dimensional Lieb-like lattice have been investigated. • Multiple compensation temperatures were discovered. The phase diagram and magnetization of a two-dimensional Lieb-like lattice consisting of magnetic atoms with mixed spins 5/2, 3/2, and 2 were investigated based on the effective-field theory with correlations. They exhibited a compensation point below their phase transition temperatures, reentrant behavior, and depressed saturation magnetization within typical parameters of exchange couplings and anisotropies. In addition, the influence of a periodically oscillating magnetic field on the dynamic order parameters of a two-dimensional Lieb-like lattice is discussed. These results can help further understand two-dimensional materials' static and dynamic magnetic properties. Ising model of two-dimensional Lieb lattice is constructured and the Static and dynamic magnetic properties have been investigated for the system.

Photocurrents of charge and spin in monolayer Fe3GeTe2

In the realm of two-dimensional materials magnetic and transport properties of a unique representative $-$ Fe$_3$GeTe$_2$ $-$ attract ever increasing attention. Here, we use a developed first-principles method for calculating laser-induced response to study the emergence of photo-induced currents of charge and spin in single-layer Fe$_3$GeTe$_2$, which are of second order in the electric field. We provide a symmetry analysis of the emergent photocurrents in the system finding it to be in excellent agreement with ab-initio calculations. We analyse the magnitude and behavior of the charge photocurrents with respect to disorder strength, frequency and band filling. Remarkably, not only do we find a large charge current response, but also predict that Fe$_3$GeTe$_2$ can serve as a source of significant laser-induced spin-currents, which makes this material as a promising platform for various applications in optospintronics.

Design issues of Rotational Single Sheet Tester for Fe-Based Nanocrystalline Alloys at High Frequencies

Measuring the vector magnetic properties of nanocrystalline soft magnetic materials at high frequencies is of great significance to the optimal design and energy saving of the electrical equipment. In this paper, some key design issues are discussed for a rotational single sheet tester (RSST) to further studied the Two-Dimensional (2D) magnetic properties of nanocrystalline alloys in the kilohertz range. Firstly, the magnetization uniformity of the testing sample is analyzed and discussed considering the stray field. Secondly, the magnetizer

Two-Dimensional AC Magnetic Properties of Electrical Steel Sheet with Two-Dimensional DC-Biased Magnetization

To estimate the magnetic properties with two-dimensional AC-magnetization with two-dimensional DC-biased magnetization, three different grades of non-oriented electrical steel sheets with two-dimensional DC-biased magnetization were prepared. As a result, in the high grade specimen, the difference in the magnetic properties depending on the excitation direction (AC excitation direction is parallel to DC excitation direction) was larger than in the low grade specimen, and the magnetic properties were the best when the excitation direction was the rolling direction. Non-oriented electrical steel sheets have small magnetic anisotropy. High grade non-oriented electrical steel sheets have a large magnetic anisotropy to compare with low grade non-oriented electrical steel sheets. It is thought that magnetic anisotropy increased in the high grade non-oriented electrical steel sheets because the B-H loops under DC-biased magnetization were minor loops. In addition, the increase rate of the H widths and the increase rate of the iron losses depending on the excitation direction were relatively consistent. Since the iron loss is proportional to the area of the B-H loop, it is considered that the iron loss increased at the same rate as the H width of the B-H loop.

First-principles explorations on P8 and N2 assembled nanowire and nanosheet

‘Bottom-up’ method is a powerful approach to design nanomaterials with desired properties. The bottle neck of being oxidized of phosphorous structures may be conquered by cluster assembling method. Here, we used P8 and N2 as assembling units to construct one-dimensional (1D) nanowire (NW) and two-dimensional (2D) nanosheet (NS), the stability, electronic and magnetic properties of these assembled nanomaterials are investigated using density functional theory (DFT) calculations. The assembled 1D-P8N2 NW and 2D-P8N4 NS are identified to possess good stability, as demonstrated by their high cohesive energies, positive phonon dispersions, and structural integrity through molecular dynamics simulations at 300 and 500 K. Moreover, they also exhibit good anti-oxidization property. The 2D-P8N4 NS is a direct bandgap semiconductor with the HSE06 gap of 2.61 eV, and shows appropriate band-edge aliments and moderate carrier mobility for photocatalyzing water splitting. The 1D-P8N2 NW is an indirect bandgap semiconductor, and Mn doping could convert it into a dilute magnetic semiconductor (DMS) with one Dirac cone in the spin-up channel, while the vdW-type sheet composed of Mn1@1D-P8N2 NWs is a ferromagnetic metal. Our theoretical study is helpful to design stable phosphorus-based nanomaterials with diverse properties and potential applications.

Anisotropic Vector Hysteresis Simulation of Soft Magnetic Composite Materials Based on a Hybrid Algorithm of PSO-Powell.

To simulate the anisotropic hysteresis characteristics of soft magnetic composite (SMC) materials accurately, an improved vector hysteresis model was proposed and utilized to adjust the shape of hysteresis curves by introducing two parameters. These two parameters are correlated with the amplitude of the vector Everett function and the projection of magnetic flux density along different directions. An experimental platform was built to measure the two-dimensional (2-D) magnetic properties of the SMC material under rotational magnetizations. The scalar and vector Everett functions were constructed by the measured limiting hysteresis loops. A hybrid optimization strategy based on the particle swarm optimization (PSO) and Powell technique was proposed to identify the parameters of the improved model efficiently and precisely, which significantly improved the local optimization ability of the PSO algorithm. The simulated results strongly agree with the measured ones, and thus the effectiveness of the improved vector model and the parameter identification method proposed in this paper was verified.

Design of Novel High-Frequency 2-D Magnetic Properties Tester for Nanocrystalline Alloy

To broaden the applications of promising nanocrystalline magnetic materials in electrical engineering at high frequency, the materials must be characterized well at a wide range of frequencies and fields. This paper proposes a novel two-dimensional (2-D) magnetic properties tester up to 20 kHz. The finite element method is used to optimize the tester design by calculating the magnetic field distributions in the specimen and yokes. Considering the dimension and physical properties of the specimen, a particular B - H sensing structure is designed to measure the flux density and field intensity in the specimen. Furthermore, a frequency-domain feedback control system is integrated into the measurement system in order to control the waveform of flux density. Moreover, the paper discusses the factors which impact on the experimental results. This paper demonstrates that the novel tester is reliable to study the magnetic properties of materials. At last, the 2-D rotational magnetic properties of nanocrystalline alloy are preliminary measured.

Loss Estimation of Brushless Doubly-Fed Generator With Hybrid Rotor Considering Multiple Influence Factors

The brushless doubly fed generator (BDFG) has been a research focus of wind power generation due to its inherent promising features. Although it is important to consider the effect of losses on the design and analysis of the BDFG, there are a few related comprehensive studies. Moreover, a hybrid rotor is studied to improve the performance of BDFG, which brings greater challenges to the loss calculation. The aim of this paper is to propose the accuracy calculation methods of core loss and copper loss for the studied BDFG with hybrid rotor. The core loss calculation model which taken the influence of harmonics, alternating magnetization, rotating magnetization and two-dimensional magnetic property of material into account is proposed based on the analysis of the magnetic field characteristics. In order to calculate the copper loss considering the skin effect, the inductive current of the assisted cage bars which is difficult to obtain directly is calculated. The accuracy and correctness of the proposed approaches and models are validated by experimental results from a 25kW prototype BDFG with hybrid rotor. In addition, the proposed loss calculation method, especially the core loss calculation model, is also applicable to BDFG with other rotor structure which is operated by the magnetic field modulation mechanism.

Transition from Ferromagnetic Semiconductor to Ferromagnetic Metal with Enhanced Curie Temperature in Cr2Ge2Te6 via Organic Ion Intercalation.

Magnetism in the two-dimensional limit has become an intriguing topic for exploring new physical phenomena and potential applications. Especially, the two-dimensional magnetism is often associated with novel intrinsic spin fluctuations and versatile electronic structures, which provides vast opportunities in 2D material research. However, it is still challenging to verify candidate materials hosting two-dimensional magnetism, since the prototype systems have to be realized by using mechanical exfoliation or atomic layer deposition. Here, an alternative manipulation of two-dimensional magnetic properties via electrochemical intercalation of organic molecules is reported. Using tetrabutyl ammonium (TBA+), we synthesized a (TBA)Cr2Ge2Te6 hybrid superlattice with metallic behavior, and the Curie temperature is significantly increased from 67 K in pristine Cr2Ge2Te6 to 208 K in (TBA)Cr2Ge2Te6. Moreover, the magnetic easy axis changes from the ⟨001⟩ direction in Cr2Ge2Te6 to the ab-plane in (TBA)Cr2Ge2Te6. Theoretical calculations indicate that the drastic increase of the Curie temperature can be attributed to the change of magnetic coupling from a weak superexchange interaction in pristine Cr2Ge2Te6 to a strong double-exchange interaction in (TBA)Cr2Ge2Te6. These findings are the first demonstration of manipulation of magnetism in magnetic van der Waals materials by means of intercalating organic ions, which can serve as a convenient and efficient approach to explore versatile magnetic and electronic properties in van der Waals crystals.

Finite-element analysis of turbine generator using homogenization method taking account of magnetic anisotropy

PurposeThis paper aims to propose a homogenization method considering magnetic anisotropy for a magnetic field analysis of a turbine generator. To verify the validity of the proposed method, the effects of magnetic anisotropy and a space factor on a no-load saturation curve and no-load iron loss of the turbine generator are discussed.Design/methodology/approachThe proposed method was derived from the combination of the homogenization of microscopic fields in a laminated iron core with the modelling of two-dimensional magnetic properties based on free energy. To verify the validity, the proposed method was applied to a finite-element analysis of a simple ring core model. Finally, a no-load saturation curve and iron loss of the turbine generator was investigated by using the proposed method.FindingsThe computational accuracy of the homogenization method considering magnetic anisotropy is almost the same as that of the detailed modelling of the laminated structure in the magnetic field analysis of the laminated iron core. Furthermore, it is clarified that magnetic anisotropy does not have a large influence on the no-load saturation curve of the turbine generator because of the large air gap. On the other hand, the space factor affects the shape of the no-load saturation curve.Originality/valueThis paper verifies the validity of the homogenization method considering magnetic anisotropy method and elucidates the effects of magnetic anisotropy and a space factor on no-load characteristics of the turbine generator.

Two-Dimensional AC Magnetic Properties of Electrical Steel Sheet under Two-Dimensional DC-Biased Magnetization

Electrical steel sheets have been widely employed as a magnetic core material of an electromagnetic equipment. Magnetic materials in the equipment is possible to be excited by two-dimensional AC-magnetization and/or AC-magnetization with two-dimensional DC-biased magnetization. In this paper, the magnetic properties of electrical steel sheets under two-dimensional DC-biased magnetization have been researched. The phase difference of between the fundamental components of B and H under high DC-biased condition becomes very smaller and phase compensation is very important in loss measurement. Also, we found that the magnetic loss under two-dimensional AC-magnetization is very sensitive to magnetic flux density waveform.

Investigation of a measurement method of 2-D magnetic properties by means of 1-D single sheet tester

Although two-dimensional (2-D) magnetic properties can be measured by using a 2-D single sheet tester (SST), the construction of the reliable 2-D SST is considerably difficult. By contrast, the flux density and magnetic field parallel to the excitation direction can be measured in a normal one-dime nsional (1-D) SST. If the average flux density points toward the excitation direction in a specimen with any inclination angle from its rolling direction, the magnetic energy can be defined and therefore 2-D magnetic properties can be calculated by means of an energy-based modelling method. However, the direction of the flux density and magnetic field in the 1-D SST has not been deeply discussed when a specimen with any inclination angle is measured. In this paper, the behavior of the flux density and the magnetic field strength is examined by using 1-D SST. The direction of the flux density is measured by using a pair of cross B-coils. The direction of the magnetic field strength is measured by using a pair of cross H-coils. The effect of the specimen width on the distribution of flux density is also investigated by using a magnetic field analysis. As a result, when a pair of cross H-coils is adopted to a specimen with appropriate aspect ratio, 2-D magnetic properties can be measured by means of the 1-D SST.

Development of the apparatus for measuring magnetic properties of electrical steel sheets in arbitrary directions under compressive stress normal to their surface

In designing motors, one must grasp the magnetic properties of electrical steel sheets considering actual conditions in motors. Especially important is grasping the stress dependence of magnetic power loss. This paper describes a newly developed apparatus to measure two-dimensional (2-D) magnetic properties (properties under the arbitrary alternating and the rotating flux conditions) of electrical steel sheets under compressive stress normal to the sheet surface. The apparatus has a 2-D magnetic excitation circuit to generate magnetic fields in arbitrary directions in the evaluation area. It also has a pressing unit to apply compressive stress normal to the sheet surface. During measurement, it is important to apply uniform stress throughout the evaluation area. Therefore, we have developed a new flux density sensor using needle probe method. It is composed of thin copper foils sputtered on electrical steel sheets. By using this sensor, the stress can be applied to the surface of the specimen without influence of this sensor. This paper described the details of newly developed apparatus with this sensor, and measurement results of iron loss by using are shown.

A New Magnetizer for Measuring the Two-Dimensional Magnetic Properties of Nanocrystalline Alloys at High Frequencies

Nanocrystalline alloys are used extensively in high-frequency electromagnetic applications for their low magnetic losses and high saturation flux densities. To characterize their vector magnetic properties over a broad frequency range, a new magnetizer with a compact flux density-field B-H sensor was developed for two-dimensional testing up to 10 kHz.

Comparison of rotational single sheet testers for evaluating 2-D magnetic properties of electrical steel sheet

Evaluating magnetic properties accurately under various flux conditions is necessary to reduce iron losses in designing motors and transformers. Particularly, two-dimensional (2-D) magnetic property is one of the most important factors for highly eff

Computation of Electromagnetic Losses in Double-Rotor Vernier PM Motors with Three Topologies Using TS-FEM

This paper focuses on the electromagnetic losses computation and comparative analysis of the proposed three topologies vernier permanent-magnet (VPM) motors by using time-stepping finite element method (TS-FEM). A dynamic core loss model of numerical analysis considering two-dimensional (2-D) magnetic properties to grasp the magnetic phenomenon inside the motors is adopted to compute the core losses of the three VPM motors. The core loss model can provide reasonable accuracy and all necessary parameters are either directly available or extracted from manufacturer-provided loss curves. The flux distribution, copper losses, core losses and efficiency of the three proposed VPM motors have been investigated, and the core loss is the important loss part of the proposed flux-modulation VPM motors.

Two-dimensional magnetic property measurement for magneto-rheological elastomer

Magneto-rheological elastomer (MRE) is a new kind of smart material. Its rheological properties can be altered and controlled in a real time manner when it is applied an external magnetic field. For calculating magnetic properties of MRE material, usually Maxwell-Garnet equation is used to acquire an approximately effective permeability. This equation treats the magnetic property of particles as linear. However, when the applied magnetic field is alternating or rotating, the nonlinearity of magnetic property and magnetic hysteresis cannot be neglected. Hence, the measurement and modelling of the magnetic properties under alternating and rotating magnetic fields are essential to explore new applications of the material. This paper presents the investigation on the magnetic hysteresis properties of MRE material under one-dimensional (1-D) alternating and two-dimensional (2-D) rotating magnetic field excitations. A kind of MRE material, consisting of 70% carbonyl iron particles, 10% silicone oil, and 20% silicone rubber, was used to investigate the magnetic properties. The diameter of carbonyl iron particles is 3–5 μm. The measurement results, such as the relations between magnetic field intensity (H) and magnetic flux density (B) under different magnetic field excitations on the MRE sample, have been obtained and analyzed. These data would be useful for design and analysis of MRE smart structures like MR dampers.

Development of Transducer for Measuring Two-dimensional Local Vector Magnetic Properties

Development of Transducer for Measuring Two-dimensional Local Vector Magnetic Properties

Modeling of Two-Dimensional Magnetic Properties Based on One-Dimensional Magnetic Measurements

This paper proposes a modeling method of two-dimensional (2D) magnetic properties based on magnetic energy obtained from several one-dimensional (1D) magnetic properties with different inclination angles from rolling direction. We compare the measurement results of non-oriented electrical steel sheets by 2D and 1D single sheet testers (SSTs) and confirm that almost the same magnetic properties can be obtained from each tester. Based on several 1D magnetic properties measured by the 1D-SST, we evaluate a magnetic energy by using a Fourier series expansion. By differentiating the estimated magnetic energy, we can obtain the perpendicular components of magnetic field with respect to the magnetic flux density which cannot be measured by the 1D-SST. In order to confirm the validity of the proposed method, we compare the estimated 2D magnetic properties with measured ones. Finally, the calculation procedure of the Jacobian matrix is presented and the proposed method is applied to the finite element analysis.

Measurement of Local Vector Magnetic Properties in Laser Scratched Grain-Oriented Silicon Steel Sheet With a Vector-Hysteresis Sensor

This paper presents measured local vector magnetic properties in a transformer type model core made of a laser-scratched grain-oriented electric steel sheet by using a vector-hysteresis (V-H) sensor. The V-H sensor consists of B-needle probes for measurement of the magnetic flux density vector <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> and double H-coil for measurement of the field strength vector <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> . The distance between the B-needle probes was shortened to be 2.5 mm and a 2 mm × 2 mm-sized double H-coil was mounted on the sensor head to realize higher resolution. The measurement accuracy of the B-needle probes was confirmed with a spatial probe, which can change the needle distance from 2 mm to 20 mm. The results show that the detailed local two-dimensional vector magnetic properties depending on laser-scratches are measurable with the developed new sensor.