Naturally-occurring Ilmenite ore is usually a mixture of Ilmenite (FeTiO₃) and hematite (Fe₂O₃). Synthesized solid solutions of Ilmenite and hematite are known to have interesting magnetic and electric properties. In the present study, we report that naturally occurring Ilmenite sintered with titanium dioxide also has low electrical resistivity and can be a natural resource for applications as electronic materials as envisaged for the system Ilmenite-hematite.

Single-phase (GdNi)_x(BiFe)_1-x O₃ (x = 0, 0.025, and 0.05) nanoparticles of 30-40 nm particle size on average were fabricated using a sol-gel method. Transmission electron microscopy, X-ray diffraction as well as Raman spectral measurements and analyses revealed that the (GdNi)_x(BiFe)_1-xO₃ nanoparticles undergo a structural transformation from the rhombohedral R3c structure (for x = 0 and 0.025) to the triclinic P1 (for x = 0.05). X-ray photoemission spectroscopy served to confirm that co-doping of Gd³⁺ and Ni²⁺ ions decreases oxygen-vacancy concentration, reflecting less Fe²⁺ content in the co-doped samples compared with pure BiFeO₃. Magnetization hysteresis loops showed that the magnetization value for x = 0.05 at 50 kOe increases significantly to M = 5.32 emu/g at 300 K and to 14.47 emu/g at 5 K, representing 760 and 690 % enhancements relative to those for x = 0. Fitting of the Curie-Weiss law to the observed magnetization-versus-temperature curves indicated the presence of weak ferromagnetic coupling in the samples. We also noted the exchange bias effect in the nano-size particles, possibly originating from exchange coupling between surface spins of an uncompensated ferromagnetic nature and core spins of an antiferromagnetic nature. We ascribed these significant improvements in the Gd-Ni-co-doped BiFeO₃ nanoparticles’ magnetic properties to the rhombohedral R3c to triclinic P1 structural transformation, due to the samples’ particle size being smaller than the modulation length of the canted antiferromagnetic ordering of the Fe³⁺ spins. These enhanced magnetic properties, notably, might prove useful for a variety of spintronic applications.

In this paper, the unsteady of magnetohydrodynamics (MHD) second grade fluid in a porous medium due to non–coaxial rotation is investigated. The effects of heat and mass transfers (double diffusion) through an oscillating disk are considered. The non–dimensional governing momentum, energy and mass equations are obtained by using the suitable non–dimensional variables. The Laplace transform method is used to obtain the exact solutions of non–dimensional velocity, temperature and concentration profiles. The expressions of skin friction, Nusselt number and Sherwood number are also presented. The numerical result for all fluid flow profiles are plotted in graphs for the different parameters studied. The results also show that, velocity for present solution (with heat and mass transfers) has a significant impact on the velocity profiles in non-coaxial rotation due to exhibits high thermal diffusivity and thermal conductivity. The obtained exact solutions are found to be identical to the Guria [10]. It is worth mentioning that, the exact solutions are in excellent agreement with the numerical solutions of Inverse Laplace transform obtained by Gaver-Stehfest algorithm.

Accurate magnetic force calculation is essential to effectively analyzing a system or device containing magnets. Among several approaches used in the interacting magnetic force calculation of permanent magnets, equivalent magnetic charge and equivalent magnetizing current models are widely adopted. In this paper, we choose cubes and cylinders as calculating objects to investigate the detailed calculation procedures. Higher calculation accuracy of the equivalent magnetizing current model is verified by comparison between simulation and experiment results. Furthermore, we analyze the relations between two models and discriminate their equivalence in the magnetic force calculation respectively at both micro and macro scale. Reference basis for choosing a proper model to calculate magnetic force is provided in this work, which is beneficial for the design of electro-mechanical structures with permanent magnets.

In this work, the dynamic behavior of a spin valve oscillator with a Nickel-free layer, modeled by the Landau-Lifshitz-Slonczewski equation is studied. It is considered a constant applied field and a spin current with two components, a constant term and a term with a time-dependent harmonic modulation. Techniques to characterize dynamic behaviors of systems, such as Lyapunov exponents, bifurcation diagram, phase portraits, time series, and Fourier spectra were used. It is demonstrated that the system presents multiple transitions between chaotic and regular states when the constant magnetic field, the magnitude, and frequency of the alternating current are varied. Furthermore, it is found that the effect of the magnetic field and the amplitude of the currents play a meaningful role in the chaotic behavior start.

A most probable failure point update method is proposed to obtain an accurate reliability-based design of electromagnetic devices or systems in the presence of uncertainties. The first-order reliability method has been recently adopted to solve electromagnetic design problems. However, its result could be very erroneous especially for nonlinear or multi-dimensional performance functions. To overcome the drawback, a three-step computational procedure is additionally executed to ensure prescribed design feasibility at an optimum obtained from the conventional first-order reliability method: failure rate calculation, reliability index update, and most probable point update. A mathematical example and a blushless DC motor design problem are provided to demonstrate numerical accuracy of the proposed method by comparison with the conventional method.

The structural, half-metallic (HM) and magnetic properties of the imperfect Pb₂FeReO₆ containing eight different inherent defects of the Fe_Re or Re_Fe antisites, Fe1-Re1 or Fe1-Re4 interchanges, V_Fe, V_Re, V_O or V_Pb vacancies have been studied by first-principles calculations. No obvious structural changes are observed for Fe_Re or Re_Fe antisites, Fe1-Re1 or Fe1-Re4 interchanges and V_Pb vacancy defects, however, the six (two) nearest neighbors O (Fe or Re) of the vacancy move away from (close to) V_Fe or V_Re (VO) vacancies. The HM character is maintained for Fe_Re or Re_Fe antisites, far Fe1-Re4 interchange, V_Fe, V_O or V_Pb vacancies, while vanished for near Fe1-Re1 interchange or V_Re vacancy. So the near Fe1-Re1 interchange or V_Re vacancy defects should be avoided to preserve the HM character of the Pb₂FeReO₆ and thus usable in spintronics devices. Except for the Fe_Re antisite case with a slightly higher total moment, the total moments μ_tot of the imperfect Pb₂FeReO₆ with the other seven inherent defects are smaller than 3.96 μ_B/f.u. of the perfect Pb₂FeReO₆.

The magnetic flux leakage (MFL) method is the most widely used and cost-effective inspection technique for oil pipeline. However, noise is inevitable in the process of data collection; thus, the image enhancement method can be more intuitive to identify the defects in an oil pipeline MFL inspection. In this paper, the bidimensional empirical mode decomposition (BEMD) method has been used to study oil pipeline MFL images. The MFL image is decomposed into a finite number of two-dimensional intrinsic mode functions (BIMF) and a residual component by the BEMD. The wavelet transform (WT) was used to remove the noise in the BIMF. The image was then reconstructed by retaining the basic information and removing the noise. The results show that the noise is effectively removed and the detail of the MFL image is well preserved. Thus, the BEMD with WT method for oil pipeline MFL image enhancement is better than the mean filtering method and the WT method.

Parallel magnetic resonance imaging (pMRI) can acquire high temporal resolution to obtain anatomical images. Among the parallel-imaging techniques, sensitivity encoding (SENSE) is the most widely used. During the SENSE process, they are previously limited by signal-to-noise ratio degradation and aliasing artifacts owing to the subsampling effect. Therefore, the objective of this study was to develop and evaluate a novel nonlocal total variation (new-NLTV) noise reduction algorithm in pMRI with SENSE reconstruction in both simulation and experiments. According to the results, the proposed algorithm was able to achieve impressive results using quantitative evaluation factors in simulation and real phantom images. The contrast-to-noise ratio and coefficient of variation for the algorithm, in particular, were 8.24 and 7.15 times better, respectively, than those of the noisy image in the phantom study. In conclusion, this study successfully demonstrated the effectiveness of the new-NLTV noise reduction algorithm in pMRI with SENSE reconstruction.

This review paper provides a survey of material development of perpendicular recording (or perpendicular magnetic recording, PMR) as it relates to the ‘areal density’ of hard disk drives (HDDs) with high amounts of information stored per unit area. Conventional longitudinal recording has reached its limits in terms of increasing the areal density. Hence, perpendicular recording promises to achieve high areal density, which is the current goal for both the academic and industrial sectors. Development of perpendicular recording can be considered in terms of the 3 primary parts of HDDs: the medium, write head and read head. Experimentation and computer simulations were used to optimize the parameters for improving the areal density of HDDs.

The paper addresses the issue of the working point migration in non-linear permanent magnets (PM). Starting from the considerations of energy, a novel working-point migration (WPM) model is proposed which can be incorporated into a magnetic equivalent circuit (MEC). The basic theory of working-point migration is discussed which focus on the second quadrant of the magnetic hysteresis loop. The calculation method of the WPM model is proposed based on the relationship between the recoil line model and the affine transformation hysteresis loop. The establishment method for the resultant working point is described by combining the demagnetization curve and the recoil line models in the minor hysteresis loop. The static characteristic of a bistable polarized magnetic system (BPMS), as used in actuators, is calculated using the magnetic circuit method based on the WPM, while a finite element model (FEM) is also derived. The calculation method for the WPM used in MEC is also discussed. The WPM based MEC model yields reasonable results, compared with FEM, of the latching force but with much faster calculation speeds. Furthermore, the working-point state of the PM is clearly illustrated. The test system of the BPMS prototype is established. The test data and WPM model calculation results are compared. It is shown that the WPM model provides accurate prediction of static characteristics of an electromagnetic system.

To improve the test efficiency and reduce the test cost, this paper presents a design method of universal power-hardware-in-the-loop (PHIL) simulator for brushless DC motor (BLDCM) and permanent magnet synchronous motor (PMSM). The actual stator winding is simulated by the power-level current source in the simulator, thus, the electric power can be interacted between the simulator and the motor driver. By the method of bilinear transform and inverse Z-transform, the line voltage based numerical models of the virtual motors are derived. Moreover, the relationship between the line voltage and phase current of the virtual motors is analyzed, which is used to calculate the phase current commands in the numerical models. Furthermore, the universal PHIL simulator is implemented and the real-time simulation is performed, and then the offline simulation with MATLAB software and the actual motor test are also performed to verify the simulator results. The simulation and experimental results show that both PMSM and BLDCM can be simulated accurately at the power level without changing any hardware of the motor driver and the simulator.

This paper presents a new rotor design with assembled permeable retaining sleeve (APRS) to improve performances of a high speed permanent magnet synchronous machine (PMSM). The APRS consists of equal number of permeable and nonmagnetic parts, which are alternately arranged and assembled together circumferentially via keyways. Electromagnetic and mechanical characteristics of the rotor applied to a high speed flywheel PMSM are analyzed using finite element method. Machine performances are compared to an original design with commonly used rotor structure. It shows that phase inductance of the high speed machine increases dramatically due to smaller effective air gap, which may benefit suppressing inverter current harmonics. Also, permanent magnet usage reduces by 9.4 % to obtain identical back electromotive force and torque constant. In addition, a smaller skin depth owing to high-permeability material and the circumferential segmentation of the retaining sleeve effectively reduce rotor eddy current. Associated loss decreases by 40.7 % under open-circuit condition. A prototype rotor is fabricated and preliminary experimental tests are performed to confirm the analysis results.

Signal uniformity a criterion for providing objective information for evaluating the performance of a magnetic resonance imaging (MRI) and is an important measurement standard for evaluating the homogeneity of MRI system. In the early, magnet bore was very narrow in diameter. In general, magnetic bore was used with a small size that only allowed a brain imaging. Because, magnet bore size and homogeneity are inversely proportional. Recently, cylindrical-bore MR imagers with wider bores have been developed to provide higher field strengths. We compared the uniformity of large field of view (FOV) and image quality of large phantom imaging between spin echo (SE) and gradient echo (GRE) using 60-cm conventional-bore and 70-cm wide-bore 3.0 tesla (T) MR scanners. In the results, the SE and the GRE images demonstrated almost identical signal intensity patterns. The w ide bore offers similar to uniformity in the large FOV compare w ith conventional bore. Wide-bore MRI using a large FOV can provide comparable image quality and geometric accuracy to conventional-bore MRI

Nd-Fe-B-type die-upset magnet with high electrical resistivity was fabricated by hot-deforming the mixture of melt-spun Nd-Fe-B-type flakes (MQU-F: Nd_13.6Fe_73.6Co_6.6Ga_0.6B_5.6) and Dy-containing salts: eutectic (DyF₃–LiF) salt mixture and DyF₃ single salt. Profound electrical resistivity enhancement was feasible in the Nd-Fe-B-type die-upset magnet by adding Dy-containing salts. More profound electrical resistivity enhancement was achieved in the magnet added with dielectric eutectic (DyF₃–LiF) salt mixture with respect to the magnet added with single DyF₃ salt. This was attributed to better electrical insulation between the flakes by forming more continuous coverage of the flake interface with the easily melted dielectric salt. Coercivity of the die-upset magnet was also profoundly enhanced by optimal addition of Dy-containing salts, and this was attributed to substitution of some Nd in the Nd₂Fe₁₄B-type grains near flake surface by Dy atoms from the added salt. Kerr microscopy revealed that for both the magnets with or without salt addition, formation of reverse domain initiated mostly inside the flake. Reversed domain started to form at higher reverse field for the magnet added with Dy-containing salt than for the magnet without salt addition. Practical demagnetization occurred largely by formation of new reverse domains at random places rather than enlargement of previously formed reverse domain for both the magnets with or without salt addition.

Soft magnetic composites (SMC) based on FeSiB amorphous alloys have been widely used in various electric devices. However, the amorphous powders are difficult to press, and the prepared cores exhibit low mechanical strength with high porosity. In this work, untreated and phosphated Fe powders with mean particle size of 70 μm were added into FeSiB powders with mean size of less than 25 μm to improve the performance of the SMC. The FeSiB/Fe SMCs are fabricated by cold pressing. The results show that the amplitude permeability of FeSiB/Fe SMCs increases with the increase of Fe content. However, the addition of untreated Fe powder leads to increased magnetic loss. On the contrary, the addition of phosphated iron powder can not only enhance the amplitude permeability but also effectively reduce the core loss. Hence, the addition of phosphated iron powder provides a good way to modify the soft magnetic properties of FeSiB/Fe SMC for AC application.

Regulation of the efficiency of electric motors worldwide has recently been tightened further because the contribution of electric motors to overall energy consumption cannot be denied. For many years, induction motors have fulfilled tasks in various fields of industry; however, alternative motors have also been gaining attention to realize more cost-effective motors over the long term. It is foreseen that induction motors (IMs) may not be replace-able in single-speed applications, excluding a few special applications; however, applications for which the variation of speed is required offers opportunities for the entry of other motor technologies. Synchronous reluctance motors (SynRMs) are one option that could provide such benefits. This paper provides the experimental results of SynRMs which, under the rated condition, aim to satisfy the IE4 efficiency class. Five Syn-RMs ranging in power through 5.5, 15, 37, 75 to 132 kW have been manufactured and tested for experimental comparison with IMs of equivalent output power.

Sintered Ni_0.4Zn_0.6Fe₂O₄ ferrite with various additives, namely, CoO, Cu₂O, SiO₂, CaCO₃, and MgO was prepared by conventional ceramic processes. The formation of a single-phase cubic spinel structure was confirmed by powder X-ray diffraction. The microstructure and magnetic properties of the samples were significantly changed by the type of additive. In the frequency-dependent complex permeability (μ', μ") measurement, it was found that Cu₂O and CoO were more effective than the other additives for modulating the μ', μ" spectra. This was because a larger spectrum shift, either to a lower or higher frequency, could be achieved by the same doping amount of 1 wt.%. When the doping amount of CoO increased up to 3 wt.%, the μ', μ" spectra gradually shifted to a higher frequency following Snoek’s limitation law. The co-doping of 1.5 wt.% CoO and 0.5 wt.% Cu₂O was more effective for radio-frequency identification (RFID) applications than any individual doping because a relatively large real part of the permeability (μ' = 125.3) and small loss factor (μ" = 5.8) could be achieved simultaneously at the frequency of 13.56 MHz.

The Magnetic fluid is a new type of magnetic material. It is a colloidal liquid made of nanoscale ferromagnetic particles suspended in a carrier fluid. Magnetic fluid sealing is one of the most successful applications of the magnetic fluid. As a new type of seal with the advantages of no leakage, long life and high reliability, magnetic fluid seal has been widely used under vacuum and low pressure differential condition. Two types of permanent magnets, the annular permanent magnets and the cylindrical magnets, are usually used in magnetic fluid seals in engineering. However, the influence of permanent magnet structure on sealing capacity was not clear, hence a new experimental setup was designed in order to study the influence of permanent magnet structure on sealing capacity. The annular permanent magnets and the cylindrical magnets were used as the magnetic source of the experimental setup in a series of tests respectively. The relationship between the sealing capacity of magnetic fluid seal and the end-face area, axial length of the magnet was analyzed by the electromagnetism theories and theoretical derivation. The result of the experiments shows that the sealing capability grows with the end-face area of the magnet, and the growth rate becomes much slower when magnet end-face area attains a certain value; the reluctance of pole pieces and shaft can’t be ignored when magnetic field attains a certain value; the modified theoretical formula had a good match to the measured values when the end-face area of the magnet is small enough to ignore the reluctance of pole pieces and shaft.

The magnetic properties of Zn₂TiO₄ single crystals were investigated by physical property measurement system (PPMS). The field dependent magnetization (M-H) curves showed a weak ferromagnetism at low field and diamagnetism at high field for Zn₂TiO₄ single crystals. The zero-field-cooled (ZFC) and field-cooled (FC) curves further confirmed ferromagnetic behavior of the sample. With the temperature decreasing from 300 to 10 K, the weak ferromagnetism increased slowly. Around 50 K, the M-T curves had a shoulder. After the temperature decreased to 10 K, the ferromagnetism increased significantly. The magnetic mechanism was investigated using the first-principle calculations method. The origin of the ferromagnetic was discussed.

Magnetic sensors are essential sensing elements in various industrial applications, but the design and technology used in the development of these sensors vary from application to application. Recently Surface Acoustic Wave (SAW) sensors have gained considerable attention due to their advantages over conventional sensors. SAW sensors are a class of Microelectromechanical (MEMS) system that use SAW technology and can be easily configured to sense physical parameters including magnetic fields. This paper presents an overview of recent research in the domain of magnetic field sensing based on such SAW devices. The paper describes the most common design approaches in practice and also discusses the key properties of fabrication materials for optimum design and performance. A short review of the processes involved in the development of SAW magnetic sensors is also covered in this paper.

To solve the problem of wall thickness reduction and defects of oil and gas pipeline caused by corrosion or erosion, a remote field eddy current (RFEC) testing method with coaxial double coil structure is proposed to detect corrosion residual wall thickness of oil and gas gathering pipelines. Based on electromagnetic field theories, RFEC technology is theoretically analyzed. The theoretical model of RFEC detection for coaxial double coil structure is established. The relationship between the voltage phase of detection signal and the wall thickness of pipeline is derived, and an evaluation method of the residual wall thickness of the pipeline based on the phase trough time of the RFEC detection signal is proposed. The parameters of RFEC probe are optimized by Finite Element Method, and the detection system is designed on the basis of it. The practicability and the correctness of the theoretical model of the detection system are verified by experiments. It can be used to detect the residual wall thickness of pipelines in real time under different media conditions.

To investigate the effects of repetitive transcranial magnetic stimulation (rTMS) to the anterior cingulate cortex (ACC) area on changes in psychological aspects in chronic lower back pain patients. Twenty-one subjects were randomly assigned to control group (n=10, both general physiotherapy and sham rTMS) and experimental group (n=11, both general physiotherapy and rTMS). Each group received treatment (physiotherapy : 20 minutes, 10 Hz rTMS : 10 minutes) five days per week for 4 weeks. Assessment of psychological aspects was measured pre, post, and 2 week follow up after treatment. The comparison results with regard to heart rate variability (HRV), EEG (α wave), Beck Depression Inventory version (K-BDI), Fear of Daily Activities Questionnaire (FDAQ), and Fear-Avoidance Belief Questionnaire (FABQ) confirmed that experimental group had a greater recovery to positive levels in comparison to control group. As a results, the application of rTMS to the ACC together with physiotherapy can have a positive effect on pain-related psychological aspects.