Crystallographic and magnetic characteristics of thin-film Ni_0.5Co_0.5Fe₂O₄ ferrimagnet prepared by a sol-gel deposition method were investigated by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and vibrating sample magnetometry (VSM). The mixed ferrite Ni_0.5Co_0.5Fe₂O₄ specimen was found to be polycrystalline having cubic spinel structure with slightly reduced lattice constant compared to CoFe₂O₄. The XPS data indicate that Co and Ni ions in Ni_0.5Co_0.5Fe₂O₄ have charge valence of +2. The VSM measurements indicate that the Ni_0.5Co_0.5Fe₂O₄ film have saturation magnetization, remanent magnetization, and coercivity of 257 emu/cm³, 115 emu/cm³, and 0.5 kOe, respectively, which are 62 %, 68 %, and 29 % of those of CoFe₂O₄. The reduction of the magnetic parameters of Ni_0.5Co_0.5Fe₂O₄ compared to CoFe₂O₄ is primarily attributable to the smaller magnetic moment of high-spin Ni²⁺ ion (2 µ_B) than that of Co²⁺ ion (3 µ_B).

Fabrication of thin films is crucial in the study of fundamental properties of matter and designs of devices. In this work, multiferroic dysprosium manganites DyMnO₃ thin films were grown epitaxially on SrTiO₃ (001) and yttrium stabilized zirconia (111) [YSZ (111)] substrates by pulsed laser deposition technique. The fabricated films showed perfectly orthorhombic crystallization on SrTiO₃ (001) and hexagonal crystallization on YSZ (111) substrates. At low temperatures, the magnetic measurements revealed three magnetic transitions at 10 K, 21 K and 43 K for orthorhombic DyMnO₃ film, 7 K, 38 K and 58 K for hexagonal DyMnO₃ film, respectively. The results are consistent with those observed in bulk materials, corresponding to magnetic ordering of the Dy³⁺ ion spins, antiferromagnetic transitions and spin reorientation respectively. This work provides a convenient method to manipulate the film structure by choosing suitable substrates, and it can be used in the study of magnetic properties of multiferroic manganites and related device fabrication.

Herein, a ferromagnetic cobalt (Co) film was deposited on a VO₂ film exhibiting a structural phase transition from monoclinic to tetragonal at ~340 K to investigate the magnetoelastic effect caused by a phase-transition-induced strain. First, (100) and (101) VO₂ films with thicknesses of 11-43 nm were grown on Al₂O₃ using pulsed laser deposition, and 2.5-nm-thick Co films were deposited on top of them via sputtering. The magneto-optic Kerr effect hysteresis loops were measured with the temperature variation across the structural phase transition temperature of VO₂. Upon heating, an increase in the coercive field of the Co layer was observed at the structural phase transition temperature of VO₂, suggesting a magnetoelastic coupling between the Co and VO₂ layers. The coercive field increment diminished with decreasing VO₂ thickness, and it disappeared as the VO₂ became thinner than a critical value of ~11 nm. These results imply that a phase-transition-induced strain in the VO₂ layer can be used to change the coercive field of the neighboring magnetic layer.

The effect of two-stage sintering of composition ceramics between (0.6)Mg_0.7Zn_0.3Fe₂O₄ and (0.4)Ba_0.7Sr_0.3TiO₃ on crystal structure, microstructure, electrical and magnetic properties was studied. Samples were sintered using a two-stage sintering method with the first sintering temperature (T₁) at 1350 ℃ with different holding times for 30, 50 and 60 min and cooled down to the second sintering temperature (T₂) with sintering temperatures at 900 ℃ and 1100 ℃ for 5 h with heating/cooling rate at 10 ℃/min. It was found that the densities and shrinkage values tended to slightly increase with the length of holding times at T₁. XRD patterns showed a combination phase between Mg_0.7Zn_0.3Fe₂O₄ and Ba_0.7Sr_0.3TiO₃. The crystallize size and lattice strain were calculated from XRD patterns and found to increase with T₂ sintering. EDX analysis was used to confirm the elemental composition percentage of (0.6)MZF-(0.4)BST. Examination of the microstructure of composition ceramics with SEM revealed grain sizes in the range of 0.852-1.877 μm; with, square shaped grains corresponding to the Mg_0.7Zn_0.3Fe₂O₄ phase and round oval shape corresponding with Ba_0.7Sr_0.3TiO₃ phase. Magnetic behavior and dielectric constant are obviously increased with highly dense ceramics. Finally, the optimal conditions of two stage sintering were obtained for the holding times of T₁ about 50-60 min and the second sintering temperature of T₂ at 900 ℃ for 5 h.

We fabricated pure-phase BiFeO₃ (BFO) and MnFe₂O₄ (MFO) nanoparticles as well as their nanocomposites (BMFO), and then we studied their structures and magnetic properties. Pristine BFO nanoparticles of 93.3 nm average diameter were successfully synthesized using the sol-gel method by varying the solvent condition and the precursor amount. Pristine MFO nanoparticles with a mean diameter of 70.5 nm were synthesized using the co-precipitation method entailing the optimization of the preheating and aging steps. The fabricated MFO nanoparticles showed mostly nanospheres with few nanocubes. The nanocomposite samples of 50 % MFO and 50 % BFO were fabricated through grinding and pelletization, followed by sintering under an inert atmosphere. The crystal structures of the pristine materials in the nanocomposites were well preserved. The magnetization values (M_s) of the BFO, MFO, and BMFO were 4.9, 52, and 33 emu/g, respectively. This latter M_s value was significantly higher than that of BFO, owing to the coexistence of Fe²⁺ and Fe³⁺ in its BFO phase and the incorporation of magnetic MFO. Two synthesis methods and material properties including the structural, morphological, magnetic, and oxidation states of the BFO-MFO nanocomposites were studied in order to achieve a high M_s value of 33 emu/g, which is higher than the bulk values of previously reported BFO-MFO composite samples.

We investigated how geometry affects chiral magnetic logic devices, using micro-magnetic simulation. The logical NOT gate in the device was operated by current-induced domain wall (DW) motion in perpendicularly magnetized nanowires with a locally modulated in-plane magnetic anisotropy (IMA) region, where the up-down DW is switched into a down-up DW by current. We modulated the width of the nanowires as well as the length of the IMA region and found that an optimized geometry exists which depends on the Dzyaloshinskii-Moriya Interaction. Integrating the optimized NOT-gate, we then demonstrated NAND or NOR logic operations. Our results provide design guidelines for the magnetic logic device, paving the way to functional magnetic logic-in-memory devices.

In this study, we assessed image quality and geometric accuracy as a function of the gradient physical linearity used for diffusion-weighted imaging (DWI) on both conventional-bore and wide-bore scanners. The signal to noise ratio (SNR) was calculated using b = 1000 DWI images for all acquisitions. To evaluate geometric accuracy, the diameter of a phantom on an image slice was measured in four directions. In comparison with the enhanced gradient mode, the default and maximum gradient modes showed higher SNRs with both bore sizes. There were significant differences in SNR among the various gradient modes of the two bore sizes. The geometric accuracy evaluations showed no statistically significant differences in the measured lengths among the various gradient modes and both bore sizes. The wide bore using default and maximum gradient mode showed higher SNR than the conventional bore, and comparable geometric accuracy.

The authors are equally contributed.

Negative stiffness element (NSE) has extensive uses in engineering applications, such as vibration isolation, energy harvesting, and mechanical metamaterial. However, to realize a linear negative stiffness characteristic is still a challenging task. In this paper, we present a compact magnetic negative stiffness element (MNSE) that composed of three rectangular permanent magnets and configured as repelling configuration in horizontal to realize linear negative stiffness characteristic. The effects of the MNSE configuration parameters on the negative stiffness characteristic are analyzed in detail. The results demonstrate that the magnitude of the negative stiffness characteristic can be adjusted by changing the height ratio and width ratio between the central and outer magnets. The height difference between the central and outer magnets can be used to tune the degree of nonlinearity of the negative stiffness characteristic and to get the uniformity stiffness characteristic in the equilibrium position. The procedure to realize the linear negative stiffness characteristic with the expected magnitude and displacement range is developed and confirmed. The proposed MNSE and the design procedure offer an engineering application foundation for the magnetic linear negative stiffness.

In order to obtain the maximum magnetic energy product in the sealing clearance of magnetofluid seal and improve its critical pressure, a diverging stepped magnetofluid seal with small clearance was designed based on the magnetic circuit design theory and the magnetofluid seal theory. Magnetic distribution and its theoretical critical pressure were calculated by the finite element method, which could prove the reliability of design method in the magnetic circuit. The paper studies the effects of axial clearance, radial clearance and pole tooth number on the pressure capabilities of diverging stepped magnetofluid seal in specific values, which were analyzed and compared in details. The results show that the magnetic flux leakage at the junction of the pole piece and the permanent magnet in the diverging stepped magnetofluid seal leads the theoretical critical pressure calculated by the magnetic circuit method to be lower than that calculated by the finite element method. Moreover, when the pole tooth number in the axial clearance is not less than the pole tooth number in the radial clearance, and the width of axial clearance is smaller than the height of radial clearance, the critical pressure of diverging stepped magnetofluid seal is better than that of the ordinary magnetofluid seal.

In order to improve the pressure capability of Magnetorheological fluid (MRF) reciprocating seal with four magnetic sources, MRF reciprocating seal structure was designed based on the formula of MRF reciprocating seal. The magnetic field distributons in the sealing gap of MRF reciprocating seals were analyzed by using finite element analysis of magnetic field. The influences of structure parameters such as sealing gap, ratio of permanent magnet height to length, ratio of pole tooth length to width, ratio of slot width to pole tooth width and ratio of pole piece height to the shaft radius on the sealing capabilities were studied. The results were analyzed and discussed. The results show that the pressure capability of MRF seal decreases significantly with the increase of sealing gap. The pressure capability of the MRF seal increases firstly and then decreases with the increase in the ratio of permanent magnet height to its length. The pressure capability of the MRF seal increases firstly and then decreases with the increase in the ratio of pole tooth length to its width. The pressure capability of the MRF seal increases firstly and then decreases with the increase in the ratio of slot width to pole teeth width. The pressure capability of MRF seal decreases with the increase in the ratio of pole piece height to shaft radius.

Nd in hot-deformed Nd-Fe-B magnets was partially substituted by Ce and La for the purpose of reducing the materials cost and balancing the utilization of rare earth resources. Initial melt-spun ribbons with the nominal compositions of (Nd_1-xM_x)_13.6Fe_balB_5.6Ga_0.6Co6.6 (x = 0, x = 0.2/M=Ce, x = 0.3/M=Ce, Ce+La, wt.%) were prepared by a single-roller melt-spinning method, and pulverized into powders. The powders were then hotpressed at 973 K under 100 MPa, and deformed at 973 K until 75 % of height reduction was achieved. The magnetic properties of hot-deformed magnets were decreased with the substitution of Ce for Nd. In addition, simultaneous substitution of Ce and La for Nd resulted in much lower magnetic properties. This tendency was almost the same as initial melt-spun powders. The deterioration on magnetic properties by substation of Ce and La for Nd in hot-deformed Nd-Fe-B magnets could be attributed to not only inferior intrinsic properties of (Ce/La)₂Fe₁₄B to Nd₂Fe₁₄B phase but also the effect of Ce/La substitution on microstructure such as density and grain alignment during hot-deformation. Although the magnetic properties were deteriorated by substitution of Ce and La for Nd in hot-deformed Nd-Fe-B magnets, the cost performance was largely enhanced from 2.32 to 2.62 MGOe×kg/$ by 13 % when increasing the content of Ce substituted for Nd from 0 to 0.3 wt.%.

Effective low melting-point Dy-diffusion for grain boundary diffusion treatment for enhancing coercivity in Nd-Fe-B-type magnet was found in the DyF₃–LiF binary system. Efficacy of the low melting-point (DyF₃–LiF) diffusion source as Dy-diffusion source for enhancing coercivity in the diffusion processed Nd-Fe-B-type magnet was investigated. Speedier and more profound coercivity enhancement in the Nd-Fe-B-type magnet was achieved by grain boundary diffusion using the low melting-point (DyF₃–LiF) diffusion source with respect to solid DyF₃ single salt. Since the liquid in the (DyF₃–LiF) mixture contained plenty of Dy atoms already freed from DyF₃ and they were in better contact with magnet, speedier and profuse diffusion of Dy atoms through Nd-rich grain boundary was possible in the magnet coated with low melting-point (DyF₃–LiF) diffusion source.

A series of Fe–Si–B–P amorphous alloys with high Fe content in the range of 83-85 at.% were successfully prepared through a melt-spinning technique. The effects of Fe content and metalloid elements on thermal and magnetic properties of Fe–Si–B–P amorphous alloys were studied. The saturation magnetization (M_s) values of amorphous alloys tend to decrease with the increase of Fe content higher than 83 at%. For a given Fe content, the replacement of Si or B by P results in a decrease of the v value. When the P content more than 5 at.%, the M_s value of the ribbon rapidly decreases. In addition, the compositional dependence of the thermal and magnetic properties has been discussed.

In this study, iron-based amorphous powders with two different sizes, which are the average sizes of 18.92 μm and 74.69 μm, were mixed to increase the powder packing fraction and resulting soft magnetic properties. By varying the mixing ratio, the powder packing fraction was experimentally measured and also estimated by the Desmond model and the computational simulation on the basis of the discrete element method (DEM). As a result, the DEM simulation exhibited higher validity compared to the Desmond model possibly because it accounts for the interaction between the powders, such as repulsion and aggregation, which are not considered in the Desmond equation. Finally, the maximum powder packing fraction of 73.86 % was achieved when the powders were mixed at the ratio of 5:3 (~25 μm: 45~63 μm). This ratio produced an increase of 32.5 % for coercivity and 17.8 % for saturated magnetization compared to the case of 100 % large powders with a 74.69 μm average diameter.

Fe-Si-Al soft magnetic composites were composed of gas-atomized Fe-9.6wt.%Si-5.4wt.%Al alloy powders insulated with silica nanoparticles. The influence of silica insulation content on the core’s magnetic properties was studied. It was found that increasing the silica mass ratio deteriorated the effective permeability and core loss in the frequency range of 40-120 kHz, while improved the quality factor at 100 kHz and DC-bias performance. The effective demagnetizing field reflected by density and the core’s volume resistivity may cause the variations of these magnetic parameters. Loss separation fitting was performed using the Bertotti formula, indicating that silica insulation increased the hysteresis loss and reduced the eddy-current loss. The hysteresis loss took over at the frequency lower than 120 kHz in this work. With increasing the frequency, the eddy-current loss grew more quickly than the hysteresis loss. Therefore, different methods should be adopted to reduce the core loss according to the core’s application frequency.

Multiferroic Sc-doped YFeO₃ nanoparticles were obtained by a low-temperature solid-state reaction route. It indicated that with the addition of Sc, nanosized YFeO₃ powders were obtained at 800 ℃, and the orthorhombic phase was transformed into the hexagonal structure. Magnetic hysteresis loop illustrated the magnetic property of YFeO₃ nanoparticles improved with Sc doping. The maximum magnetization of the powders was about 4.00 emu/g, showing that the energy gap can be reduced to 2.25 eV and thus the doping nanoparticles can be used in optical field. Therefore, the optical and magnetic properties of the material can be obviously enhanced with Sc doping, proving its potential application in magnetic and optical fields.

The look-up data-based modeling of switched reluctance machine and the procedure of validation of experimentally obtained static torque with statistical analysis is presented in this paper. First, the experimental setup for data collection of flux linkage and static torque is established and data is collected at an unequally spaced current and rotor position so that computation of instantaneous phase current and torque can be achieved. Second, the experimental data of static torque is compared with computed data. The computation is done in MATLAB software. Third, for numerical simulations, finite difference approximations and numerical integration schemes are used to compute co-energy and static torque profiles, respectively. The comparison is carried out in terms of different statistical parameters, including absolute and relative error distributions of the measured and computed torque profiles. A correlational study, to observe the extent to which both profiles exhibit a similar trend is also carried out. Finally, the influence of computed torque is carefully analyzed by running machine in single pulse mode and current chopping mode separately. The comparison with experimental data and the statistical analysis of results show the time efficiency, accuracy, and validity of the numerically simulated torque profiles.

FeCo nanostructures are of interest because of their high magnetization and low coercivity which are suitable for biomedical applications. However, particle morphologies are still difficult to control. In this work, the FeCo nanocubes have been prepared by a chemical reduction method using hydrazine as a reducing agent. Using only polyvinylpyrrolidone (PVP) as a capping agent without cyclohexane as previous works, the obtained particles are quite uniform in shape and air-stable, and can be facile coated with silica. Nevertheless, to obtain the uniform FeCo nanocubes, the concentration of sodium hydroxide used in the synthesis needs to be optimized. The obtained FeCo nanocubes exhibit a high saturation magnetization of 220.9 emu/g and low coercivities of around 180 Oe.

The objectives of the research are to explored the heat and mass transport over a paraboloid surface of revolution by taking the effects of Lorentz force, resistive heating and internal heat source. The dimensionless version of the model was attained via similarity transformations. Then, for solution purpose, RK scheme is utilized and performed computations for the flow fields. The influence of different physical quantities on the flow characteristics described comprehensively via graphs. It is examined that the stretching index parameter m opposes the fluid velocity and the temperature enhances for Eckert number. Moreover, significant impacts of the Schmidt number are observed for mass transfer gradient.

The power cables in underground transmission lines consist of a conductor, an insulator, and a metallic sheath. The metallic sheath serves to protect the cable from external physical impacts. When a large fault current is applied to the transmission line owing to an accident, the metallic sheath prevents the fault current from penetrating into the transmission-line current and thus enhances the reliability of the transmission line. However, owing to the alternating current flowing through the conductor, an eddy current is generated in the sheath and a loss occurs. Thus, the overall transmission efficiency is reduced. In this paper, an eddy current loss in a metallic sheath was analyzed using an analytical method, and the results thus obtained were verified by comparing them with those obtained using the finite element method. In addition, a design was proposed for reducing the eddy current loss.

In this study, a multi-physics finite element model is adopted to investigate the effect of geometric discontinuity and stress concentration on the magnetic memory method (MMM). We propose a quadratic equation to fit the stress magnetization constitutive relation in the model. The relation can be used to predict the abnormality of the geometric discontinuity and the stress concentration. Simulation results show that the magnetization on the wall of the groove is the weakest and that on the bottom of the groove is the maximum. The free boundary condition releases the stress concentration of the defect. Although the magnetization induced by stress concentration is weaker than geometric discontinuity, the signal characteristics can still be used to evaluate the defect and the stress. This work proves that the MMM is a potential method for stress distribution assessment.

A small coverage of magnetic flux density (B₁) and its inhomogeneity are intrinsic problems of conventionalsurface coils. Therefore, offset-tuned bilateral-side inductively coupled radiofrequency (RF) coils have been specificallydesigned to overcome these problems. Herein, we proposed bilateral-sided wireless coils for improvingthe B₁-field uniformity by simultaneously adding a supplemental secondary coil (s-coil) to the primary coil (p-coil)in the orthogonal direction. The offset-tuned frequency of the s-coil was evaluated and compared from 0 to+60 MHz with a +10 MHz interval at the Larmor frequency of the p-coil. Using mathematical EM modeling,we optimized the +60-MHz offset-tuned s-coil at 15.2 T. Thus, a combined coil configuration with p-coil of 655MHz and two s-coils of 710 MHz was obtained. This combined coil configuration can overcome the B₁-fieldinhomogeneity of p-coils in 15.2 T small animal magnetic resonance scanner and can be extended to overcomethe volume coil array inhomogeneity.

This paper applies two different analytical methods, i.e., the perturbation method and superposition method, to calculate the magnetic flux density distribution and the magnetic force of the active magnetic bearing (AMB) with the rotor eccentricity. These two methods are thoroughly analyzed, compared and validated by the finite element model (FEM). The perturbation method is theoretically complex while the superposition method is intuitive. The valid range of the superposition method is larger than the perturbation method. However, the superposition method requires longer computation time. The main contribution of this paper is assessing the effectiveness of two analytical methods for predicting the AMB performance with the rotor eccentricity and giving a comprehensive guideline for engineers to choose the proper analytical method to design AMB.

The focus of the work demonstrates the validation of the new shape translator taking account of leakage elements in linear oscillating generator for a series hybrid electric vehicle. By comparison and analysis using the various shapes of translator teeth, it is studied to minimization of the force ripple and increasing useful magnetic flux by equivalent magnetic circuit (EMC) and finite element method (FEM). It will be analyzed considering the leakage reluctances for a more practical and effective analysis, and design process of tubular linear reluctance generator. At last, the trapezoidal shape of translator is selected as optimal model among the proposed translator teeth in tubular linear reluctance generator. The results of this study will give elaborate information about the design rules and the performance data of linear gensets.

This study was conducted to investigate the effects of high frequency repetitive transcranial magnetic stimulation (rTMS) on gait abilities in incomplete spinal cord patients. 16 subjects were randomly assigned to each of 8 experimental and control groups. 20 Hz high frequency rTMS was applied to the experimental group for 20 minutes per day, 5 times a week for a total of 4 weeks and sham rTMS was applied to the control group. The subjects were assessed for gait abilities by 10 meter walk test (10MWT), 6 minute walk test (6MWT) and community walk test (CWT). A significant improvement in 10MWT, 6MWT and CWT was observed after intervention in the experimental group (p < 0.05), and there was a significant improvement in all evaluation items compared to the control group (p < 0.05). The results of this study suggest that high frequency rTMS applied to primary motor cortex (M1) positively affects gait abilities in incomplete spinal cord injury patients.

The present communication develops the governing expressions that describe a steady incompressible two-dimensional flow of micropolar Ferrosoferric Oxide fluid towards a stretched surface under the impact of Lorentz force (magnetic field). Ferrofluids are made out of nanoscale ferromagnetic materials suspended in a base fluid (oil, kerosene, water). The distinction between the magnetorheological fluids (MRF) and ferrofluids (FF) is the size of the materials. The materials in a ferrofluid fundamentally comprise of nanomaterials, which are suspended by Brownian diffusion and generally under normal conditions will not settle. Here, Ferrosoferric Oxide (Fe3O4) is considered as nanoparticle and water as a base fluid. The governing equations are modeled by using Tiwari-Das nanofluid model with the help of appropriate similarity transformations. Furthermore, radiative heat flux and convective boundary condition is accounted. The numerical results of the governing equations are obtained through implementation of Built-in-Shooting technique. The impact of radiation parameter, stretching ratio parameter, magnetic parameter, thermal Biot number, micro-rotation parameter, velocity slip parameter and Darcy-Forchheimer number on the flow velocity and temperature are revealed graphically and discussed. The engineering curiosity like skin friction and Nusselt number are computationally computed and tabulated.

Defect induced magnetism in a single layer graphene with Boron-vacancy complex is studied using highly precise ab initio full-potential linearized augmented plane wave (FLAPW) method. From energetics, it is most stable when Boron and vacancy are the nearest neighbor. Furthermore, we propose both paramagnetic and magnetic states, with negligible energy difference, can coexist in defected graphene. The k resolved band structure reveals that the magnetism is mainly from different occupation of very localized impurity bands. Moreover, calculated STM image associated with defect is presented to provide some hint in experimental verifications.