By means of Monte Carlo simulation, we investigate the effects of interface roughness and temperature on the exchange bias and coercivity in ferromagnetic (FM)/antiferromagnetic (AFM) bilayers. Both exchange bias and coercivity are strongly dependent on interface roughness. For a perfect uncompensated interface a domain wall is formed in the AFM system during FM reversal, which results in a very small exchange bias. However, a finite interface roughness leads to a finite value of the exchange bias due to the existence of pinned spins at the AFM surface adjacent to the mixed interface. It is observed that the exchange bias decreases with increasing temperature, consistent with the experimental results. It is also observed that a bump in coercivity occurs around the blocking temperature.

Here, we describe a dual spin valve structure with distinct switching fields for two pinned layers. A device with this structure has a staircase of three distinct magnetoresistive states. The multiple resistance states are achieved by controlling the exchange coupling between two ferromagnetic pinned layers and two adjacent antiferromagnetic pinning layers. The maximum magnetoresistance ratio is 7.9% for the current-perpendicular-toplane and 7.2% for the current-in-plane geometries, with intermediate magnetoresistance ratios of 3.9% and 3.3%, respectively. The requirements for using this exchange-biased stack as a three-state memory device are also discussed.

We studied the effect on the electronic and magnetic properties of the N defect in clean and Cu-doped wurtzite III-nitrides by using the first-principles calculations. When it is doped two Cu atoms in the nearest neighboring sites, the system of AlN, GaN, or InN with the N vacancy is energetically more favorable than that without the N vacancy site. When the Cu concentration increases, the total magnetic moment of a supercell becomes small. The ferromagnetism of Cu atom is very low due to the weak 3d-3d coupling. It is noticeable that the spinexchange interaction between the Cu-3d and N defect states is important.

The magnetic and magnetocaloric properties of Gd_1-xCe_xAl₂ (x = 0, 0.25, 0.5, 0.75) intermetallic compounds alloys have been investigated in detail for the first time. XRD patterns indicated that all the samples were crystallized in a single phase with MgCu₂-type structure (Laves phase). Ce substitution for Gd increased the lattice parameters and decreased the Curie temperature from 163 K for x = 0 to 37 K for x = 0.75. A maximum entropy change of 3.82 J/kg K was observed when a 2 T magnetic field was applied to the x = 0 sample. This entropy change decreased with increasing Ce content to 2.04 J/kg K for the x = 0.75 sample.

Nd₂Fe₁₄B permanent magnetic powders (_iH_c = 9.2 kOe, B_r = 12.2 kG) were produced by HDDR process. Their coercivity was enhanced to 12.6 kOe through the grain boundary diffusion process with dysprosium hydride (DyH_x). DyH_x diffusion process was optimized through rotating diffusion process, resulting in distinct phases rich in Nd and Dy observable by field emission scanning microscopy and transmission electron microscopy. The mechanism of coercivity enhancement that resulted in restrain the coupling effect between Nd₂Fe₁₄B grains is also discussed.

The principal objective of this study was to develop a scanning technique that helps patients reduce their anxiety and relax their physical tension in the MRI system. The study targeted 10 healthy persons with no medical history of anxiety disorder in the past and with no current clinically diagnosed anxiety disorder, as well as 10 patients who were currently experiencing an anxiety disorder during the MRI scanning. The focusing board assembly was self-manufactured to conduct a clinical experiment via MRI scans. As a method to confirm the efficacy of the experiment, the bio meter was used to measure brainwaves from the study targets that were divided into the normal person group (A), who felt no anxiety in the MRI system and the experimental group, (B) who did experience anxiety in the MRI system. The two groups were compared between the cases in which the focusing board assembly was used and not used after measurements were conducted using the model MRI system and the bio meter. According to the comparison and analysis results, low measurements of the α wave indicate highly effective relaxation of tension. In the normal person group, the α wave measurement showed almost no difference between cases in which the focusing board assembly was used and cases in which it was not used. In the experimental group, the á wave measurements were lower in cases in which the focusing board assembly was used than in cases in which the focusing board assembly was not used; this was indicative of a profound relaxation effect.

We have designed, fabricated and demonstrated a novel micro-system for programmable magnetic actuation using magnetic elliptical pathways on Si substrates. Lithographically patterned soft NiFe ellipses are arranged sequentially perpendicular to each other as stepping stones for the transport of magnetic beads. We have measured the magnetization curve of the ellipsoid (9 ㎛ × 4 ㎛ × 0.1 ㎛) elements with respect to the long and short axes of the ellipse. We found that the magnetization in the long axis direction is larger than that in the short axis direction for an applied field of ≤ 1,000 Oe, causing a force on carriers that causes them to move from one element to another. We have successfully demonstrated a micro-system for the magnetic actuation of biomolecule carriers of superparamagnetic beads (Dynabead^® 2.8 ㎛) by rotating the external magnetic field. This novel concept of magnetic actuation is useful for future integrated lab-on-a-chip systems for biomolecule manipulation, separation and analysis.

Particle size distributions in 10 nm magnetite ferrofluids are analyzed based on both dc and ac magnetic measurements. Modified log-normal distributions are used for fitting the experimental results, which allows for a proper account of the narrow distributions. The calculated average particle sizes are in good agreement with the TEM results. However the ac method gives a much narrower distribution width than that of the dc magnetization curve fit. The proposed measurements combined with the analysis methods are useful for the characterization of ferrofluids being considered for biomedical applications.

Axial Field Permanent Magnet (AFPM) generators are widely applied for the small wind turbine because of the higher power density per unit weight than that of the conventional radial field generator. It is caused by the disc shaped rotor and the stator structures. The generally used AFPM generator, AFER-NS generator, is composed of the two side’s external rotors and non-slotted stator without stator core. However, the output voltage and the output power are limited by the large reluctance by the long air-gap flux paths. In this paper, the design study of AFIR-S generator having double side’s slotted stator core is accomplished to improve the output generation characteristics. The electromagnetic design analysis and the design improvement of the suggested AFIR-S generator are studied. Firstly, the electromagnetic design analysis was done to increase the power density. Secondly, the design optimizations of the rotor pole-arc ratio of permanent magnet are accomplished to increase the output power and to reduce the cogging torque. Finally, the output performances of AFER-NS and AFIR-S generator are compared with each other. For this study, 3D FEA is applied for the design analysis because of three dimensional electromagnetic structures.

This paper presents an optimal design of a direct-drive permanent magnet synchronous generator for a smallscale wind energy conversion system. An analytical model of a small-scale grid-connected wind energy conversion system is presented, and the effects of generator design parameters on the payback period of the system are investigated. An optimization procedure based on genetic algorithm method is then employed to optimize four design parameters of the generator for use in a region with relatively low wind-speed. The aim of optimization is minimizing the payback period of the initial investment on wind energy conversion systems for residential applications. This makes the use of these systems more economical and appealing. Finite element method is employed to evaluate the performance of the optimized generator. The results obtained from finite element analysis are close to those achieved by analytical model.

This paper deals with the magnetic equivalent circuit modeling and permanent magnet (PM) performance evaluations of a pole changing memory motor (PCMM). We use a coupled transient finite element method (FEM) and Preisach modeling, which is presented to analyze the magnetic characteristics of the permanent magnets. The focus of this paper is on the evaluation of characteristics such as the magnetizing direction and the pole number of the machine under re- and de-magnetization conditions.

An inductance measurement method for interior permanent magnet synchronous machine (IPMSM) is proposed in this paper. In this method, the motor is measured at standstill condition, and only a 3-phase voltage source, an oscilloscope and a DC voltage source are required. Depending on the deductive dq-axis voltage equations in the stationary frame of reference, the dq-axis inductances at different current magnitude and vector angle can be calculated by the measured 3-phase voltages and currents. And hence, the saturation and crossmagnetizing effect of the inductances are measurable. This paper introduces the principle equations, experiment setup, data processing, and results comparison on the concentrated-winding and distributed-winding IPMSMs.

A novel laminate composite of FeCuNbSiB/FeNi /PZT is proposed, where FeCuNbSiB has a permeability of around 100000, which is much larger than that of FeNi. The high-permeability FeCuNbSiB was laminated with piezomagnetic FeNi rather than attached to its ends. It is expected that the effect produced by the high permeability will act on the whole of the piezomagnetic layer. While a FeNi layer was laminated with a FeCuNbSiB layer, the strong demagnetization produced by the latter was expected to be imposed on the FeNi layer as well as the applied fields. The distribution of applied fields was altered by the high-permeability material (both bias and ac field) and the field variation positively contributed to the ME effect in piezomagnetic/piezoelectric composites.Thus the ME voltage coefficient along with the field sensitivity were improved.

Metal-insulator type, nano-granular soft magnetic films have been reviewed from the viewpoint of high frequency magnetic materials. The formation of nano-granular structure is related to the magnitude of heat of formation of intergranule materials. Variation of the ratio of granule phase to intergranule phase in the film is found to produce various characteristics in the magnetic properties of the film. The HRTEM observation reveals that neighboring granules in the film with above 60 at.% Co, contact at considerable points and the films show soft magnetic properties which are explainable in terms of the random anisotropy model for nanocrystalline materials. Addition of Ni group elements in Co-O based films enhances their anisotropy field up to 400 Oe and they exhibit excellent frequency response of permeability. Also, large electromagnetic noise suppression effect is demonstrated as one of their potential applications.

We investigated theoretically the magnetic field dependence of the quantum optical transition of qusi 2-Dimensional Landau splitting system, in GaN and ZnO. We apply the Quantum Transport theory (QTR) to the system in the confinement of electrons by square well confinement potential. We use the projected Liouville equation method with Equilibrium Average Projection Scheme (EAPS). Through the analysis of this work , we found the increasing properties of the optical Quantum Transition Line Shapes (QTLSs) which show the absorption power and the Quantum Transition Line Widths (QTLWs) with the magnetic-field in GaN and ZnO. We also found that QTLW, γ (B)_total of GaN < γ(B)_total of ZnO in the magnetic field region B < 25 Tesla.

An array of FeCo nanotubes has been successfully fabricated in the pores of porous anodic aluminum oxide (AAO) templates by wetting templates method. The morphology and structure of the nanotube array were characterized by scanning electron microscopy, transmission electron microscopy and x-ray diffraction. The average diameter of the nanotubes was about 200 nm, and the length was more than 10 μm. Vibrating sample magnetometer and superconducting quantum interference device were used to investigate the magnetic properties of the nanotube array. Interaction between the nanotubes has been found to be demagnetizing as expected and the switching field distribution is broad.

This paper presents the characteristics of PM eddy current loss and harmonic iron loss for PM step-skewed Interior Permanent Magnet Synchronous Motor (IPMSM) with concentrated windings and multi-layered PM under the running condition of maximum torque per ampere (MTPA) and flux-weakening control. In particular, PM eddy current loss and harmonic iron loss in IPMSM have been numerically computed with threedimensional Finite Element Analysis (3D FEA), whereby IPMSM with concentrated windings and multi-layered PM has been designed to identify the optimized skew angle contributing to the reduced PM eddy current loss and torque ripples, while maintaining the required average torque. Furthermore, numerical investigation on PM eddy current loss and iron loss at MTPA and flux-weakening control has been carried-out in terms of PM step-skew.

This paper presents numerical analysis and design of high power contactless transformer with a large air-gap for moving on a guided linear track which is appropriate for high-speed train or MAGLEV. The system has the typical characteristics of large leakage inductance, small magnetizing inductance, and low coupling coefficients giving rise to lower power transfer efficiency, which have been compensated by the purposely-designed contactless transformer coupled with the resonant converter modulating with high switching frequency. In particular, the best model selected from the generated six design candidates has been applied for 3D Finite Element Analysis (FEA) investigating on iron loss to evaluate the overall system efficiency.

The rolled steels for welded structure applied tensile stress have been examined by means of magnetic Barkhausen noise (MBN) method and of a physical parameter obtained from a hysteresis loop. The behaviors of MBN parameters and coercive force with tensile stress were discussed in relation to microstructure changes. There is no change in MBN parameters and coercive force below yield strength. The coercive force rises rapidly with tensile stress above yield strength. On the other hand, the rms voltage and the peak in averaged rms voltage take a maximum around yield strength and then decreases. The magnetomotive force at peak in the averaged rms voltage shows a minimum around yield strength. These phenomena are attributed to the combined effects of cell texture and dislocation density. In addition, the behaviors of MBN parameters around yield strength may be reflected by the localized changes in strain field due to the formation of dislocation tangles.

The reduction of the Nb content in the (Fe_0.75B_0.20Si_0.05)₉₆Nb₄ bulk metallic glass (BMG) has been studied. The glass-forming ability (GFA) is reduced by decreasing the Nb content, but it can be enhanced by replacing partially Fe by Co. Furthermore, the saturation magnetization of the (Fe_0.8Co_0.2)₇₆B₁₈Si₃Nb₃ BMG is 1.35 T, being with 13% larger than that of the base alloy (Fe_0.75B_0.20Si_0.05)₉₆Nb₄. (Fe_0.8Co_0.2)₇₆B₁₈Si₃Nb₃ BMG exhibits slightly larger B₈₀₀ (the magnetic flux density at 800 A/m) and smaller core losses (20%-30%) compared with the commercial Fe-6.5 mass% Si steel.

In this work, we prepared Fe-Ni alloy nanopowders by wire electrical explosion in deionized water and ethanol. Particles size and morphology of the as-synthesized nanoparticles prepared in water and ethanol were observed by transmission electron microscopy. In both cases, the as-synthesized nanoparticles were in nearly spherical shape and their size distribution was broad. The particles prepared in the water were in core-shell structure due to the oxidation of Fe element. X-ray diffraction was used to analyze the phase of the nanopowders. It showed that the nanopowders prepared in water had γ-Fe-Ni solid solution and FeO phase. The samples obtained in ethanol were in two phases of Fe-Ni solid solution, γ-Fe-Ni and α-Fe-Ni. Bulk samples were made from the as-synthesized nanopowders by spark plasma sintering at 1000 ℃ for 10 min. Structure of the bulk sample was observed by scanning electron microscope. Magnetic properties of the as-synthesized nanopowders and the bulk samples were investigated by vibrating sample magnetometer. The hysteresis loop of the assynthesized nanopowders and the sintered bulk samples revealed a ferromagnetic characteristic.

In this study, we investigated the glass-forming ability (GFA) and magnetocaloric effect (MCE) of Gd₅₅Co₂₀Al₂₃Si₂ bulk glassy alloy. It is found that the addition of 2 at% Si is effective for extension of the supercooled liquid region (ΔT_x), the ΔT_x is 55 K for the Gd₅₅Co₂₀Al₂₅ glassy alloy, and increases to 79 K for the Gd₅₅Co₂₀Al₂₃Si₂ alloy. As a result, Gd₅₅Co₂₀Al₂₃Si₂ glassy alloys with diameters up to 5 mm were successfully synthesized. The alloys also exhibit large MCE, i.e., the magnetic entropy change (ΔS_m) of 8.9 J kg^-1 K^-1, the full width at half maximum of the ΔS_m (δT_FWHM) of 87 K, and the refrigerant capacity (RC) of 774 J kg^-1.

In the present study, we separated the marker particles from the suspending particle mixture solution using isotacho-electrophoresis technique, a novel quantitative ionic particle separation method, in the microchannel. A multiple stacking zone of the suspending particle was visualized with variations in electric field strength, pH value and concentration of the ionic solution. In particular, the electrophoretic mobility of ionic particle (fluorescein) was estimated based on the electrophoretic velocity value measured by the particle image velocimetry. As a result, isotacho-electrophoresis zones were clearly visualized as going downstream in the electric field. The particle migration velocity increased proportional to the applied voltage increase; it was also affected by the pH value variations in the ionic solution.

A wrist wearable cuffless pulsimeter with a portable and small size apparatus using Hall effect is fabricated. The analysis of the pulse wave measured by the testing product of pulsimeter is done to measure the pulse rate and blood pressure. The blood pressure obtained by the puslimeter is compared with the practical values measured by electronic or mercury liquid blood pressure meters. The detail analysis of a pulse wave measured by a wrist wearable cuffless pulsimeter detecting the changes of the magnetic field can be used to develop a new diagnostic algorithm of blood pressure applying for oriental medical apparatus.

Demagnetization for a tube sample which was made of a galvanized steel sheet was performed by applying a magnetic field with a decrement to remove the remanent magnetization of the material. An orthogonal fluxgate magnetic field sensor was used to measure a magnetic field created from a ferromagnetic material. To evaluate the remanent magnetization, the measured magnetic fields were separated into two magnetic field components by the remnant magnetization and the induced one. The horizontal and the vertical bias fields should be controlled separately during demagnetization to remove the horizontal and the vertical components of the remanent magnetization of the tube sample.

In this paper, magnetic property and magnetocaloric effect (MCE) in perovskite manganites of the type La_(0.75-X)Ce_XCa_0.25MnO₃ (x = 0.0, 0.2, 0.3 and 0.5) synthesized by using the standard solid state reaction method have been reported. From the magnetic measurements as a function of temperature and applied magnetic field, we have observed that the Curie temperature (T_C) of the prepared samples strongly dependent on Ce content and was found to be 255, 213 and 150 K for x = 0.0, 0.2 and 0.3, respectively. A large magnetocaloric effect in vicinity of T_C has been observed with a maximum magnetic entropy change (|ΔS_M|_max) of 3.31 and 6.40 J/kgK at 1.5 and 4 T, respectively, for La_0.55Ce_0.2Ca_0.25MnO₃. In addition, relative cooling power (RCP) of the sample under the magnetic field variation of 1.5 T reaches 59 J/kg. These results suggest that La_0.55Ce_0.2Ca_0.25MnO₃ compound could be a suitable candidate as working substance in magnetic refrigeration at 213 K.

Traditional magnetostrictive/piezoelectric laminate composites are generally in the regular geometries such as rectangles or disks. To explore properties of the irregular geometry magnetostrictive/piezoelectric transducer in the fundamental resonant frequency, a step dumb-bell shaped Magnetoelectric (ME) transducer is presented in this study. Both analytical and experimental investigations are carried out for the dumb-bell shaped transducer in the fundamental frequency. Comparing with the traditional rectangular transducer, the theory shows the resonant frequency of dumb-bell shaped transducer is reduced 31%, and the experiment gives the result of that is 37% which is independent of dc magnetic fields. The ratio of magnetoelectric voltage coefficient (MEVC) between the dumb-bell shaped and rectangular shaped transducers in theory is 66% comparing with that of in experiment is varying from 140% to 33% when the dc field is increased from 0 Oe to 118 Oe.