Structural and magnetic properties of Fe₅₀Mn₅₀ nanocrystalline alloys prepared by the mechanical alloying technique (using commercial Fe and Mn powders as the precursors) are studied as a function of milling time, 1 hr to 48 hrs. The nano-crystallite size and shape are examined by using scanning electron microscopy (SEM). The effect of milling time on structural characterization was investigated using X-ray diffractometer (XRD) and extended X-ray absorption fine structure spectroscopy (EXAFS). Both XRD and EXAFS studies showed that the alloying process should be completed after 36 hrs milling. Concerning the magnetic behavior, the data obtained from superconducting quantum interference devices (SQUID) exhibited both magnetic saturation (M_s) and coercivity (H_c) depend strongly on the milling time, which are related to the changes in the crystallite size and magnetic dilution.

The perpendicular magnetic anisotropy of sputtered CoFeB thin films covered by MgO was investigated by vibrating sample magnetometry. Three different Co_xFe_80-xB₂₀ alloys were studied. Under out-of plane magnetic field, the saturation field was found to increase with increasing the Co content. The magnetization and interface anisotropy energy were obtained for all samples. Both showed a marked dependence on the MgO overlayer thickness. In addition, their variations were found to be non-monotonous as a function of the Co concentration.

Shielding effects in conductive and magnetic materials were investigated as a function of properties, thickness and diameter. In this work, evaluations on passive conductive and magnetic shield specimens were achieved through experimentation set-up using 50 Hz single and three phase induction field sources. Analysis on material microstructure properties and characteristics of shielding specimens were performed with the use of vibrating sample magnetometer (VSM) and field emission scanning electron microscopy (FESEM). An induction field at 136 μT of single phase system and 50 μT of three phase systems were observed to the shield specimens with the thickness ranged of 0.2 mm to 0.4 mm. It is observed that shield specimen efficiency becomes inversely proportionate to the increment of induction fields. The decrease was attributed to the surface structure texture which relates to the crystallization and non-crystallization geometrical effects.

For the treatment of osteoarthritis, pulsed electromagnetic field stimulus has been suggested as a useful therapeutic method in rehabilitative medicine. Most studies have been performed under low-frequency and lowenergy to find out biological properties for stimulating chondrocyte with pulsed magnetic field. In this study, the effect of strong pulse magnetic field on the human chondrosarcoma cells (SW-1353) has been investigated by means of cell counting, morphologies, and gene expression of cartilage extracellular matrix genes. The SW- 1353 cells were exposed under the field intensities of 270, 100, 55, 36, and 26 mTesla during 6 hours a day in 5 consecutive days. The pulse magnetic field with an LRC oscillating signal has the pulse width of 0.126 msec and stimulation period of 1 sec. For the 270 and 100 mTesla stimulation, the cell proliferation significantly increased in 21-24% as compared with the non-stimulated cells. Gene expression of cartilage extracellular matrix genes (ACAN, COMP and COL2A1) was assayed by quantitative real time-PCR method. The ACAN gene expression showed a significant brightness, which means the increase on gene expression, compared with the non-stimulated cells. Our results suggest that the strong pulse magnetic field stimulation can be utilized to accelerate cell proliferation and gene expression on human chondrosarcoma cells.

Nickel substituted manganese ferrites, Mn_1-xNi_xFe₂O₄ (0.0 ≤ x ≤ 0.6), were fabricated by sol-gel method. The effects of sintering and substitution on their crystallographic and magnetic properties were studied. X-ray diffractometry of Mn_0.6Ni_0.4Fe₂O₄ ferrite sintered above 523 K indicated a spinel structure; particles increased in size with hotter sintering. The Mössbauer spectrum of this ferrite sintered at 523 K could be fitted as a single quadrupole doublet, indicative of a superparamagnetic phase. Sintering at 573 K led to spectrum fitted as the superposition of two Zeeman sextets and a single quadrupole doublet, indicating both ferrimagnetic and paramagnetic phase. Sintering at 673 K and at 773 K led to spectra fitted as two Zeeman sextets due to a ferrimagnetic phase. The saturation magnetization and the coercivity of Mn_0.6Ni_0.4Fe₂O₄ ferrite sintered at 773 K were 53.05 emu/g and 142.08 Oe. In Mn_1-xNi_xFe₂O₄ (0.0 ≤ x ≤ 0.6) ferrites, sintering of any composition at 773 K led to a single spinel structure. Increased Ni substitution decreased the ferrites' lattice constants and increased their particle sizes. The Mössbauer spectra could be fitted as the superposition of two Zeeman sextets due to the tetrahedral and the octahedral sites of the Fe³⁺ ions. The variations of saturation magnetization and coercivity with changing Ni content could be explained using the changes of particle size.

Mn_xFe_3-xO₄ powders have been fabricated by using sol-gel methods; their crystallographic and magnetic properties were investigated by using X-ray diffraction, scanning electron microscopy, Mössbauer spectroscopy, and vibrating sample magnetometer. The Mn_xFe_3-xO₄ ferrite powders annealed at 500 ℃ had a single spinel structure regardless of the Mn²⁺-doping amount and their lattice constants became larger as the Mn²⁺ concentration was increased. Their Mössbauer spectra measured at room temperature were fitted with 2 Zeeman sextets due to the tetrahedral and octahedral sites of Fe ions, which made them ferrimagnetic. The magnetic behavior of Mn_xFe_3-xO₄ powders showed that the Mn²⁺-doping amount made their saturation magnetization increase, but there were no severe effects on their coercivities. The saturation magnetization of the Mn_xFe_3-xO₄ powder varied from 38 emu/g to 70.0 emu/g and their minimum coercivity was 111.1 Oe.

The magnetocaloric effect and magnetization behavior have been analyzed in the double-perovskite La_0.7Ba_0.3Mn_1-XFe_XO₃ compound with the sintering temperature at 1273 K. Samples were fabricated by the conventional solid-state reaction method. X-ray diffraction measurement revealed that all the samples had a single phase in orthorhombic. Detailed investigations of the magnetic entropy behavior of the samples were discussed with the variation of T_C. The magnetic entropy changes, ΔS_M of approximately 0.36-1.14 J/kg K were obtained in the temperature range of 145-350 K for the La_0.7Ba_0.3Mn_1-XFe_XO₃ compound. The enhancement of the magnetic entropy change is believed to be due to changes in the microstructure, which changes the magnetic part of the entropy of a solid around the magnetic ordering temperature.

This paper studies the effects of the Mn-site substitution by nickel on the magnetic properties and the magnetocaloric properties of La_0.7Ca_0.3Mn_1-xNi_xO₃ (x = 0, 0.05 and 0.1). The orthorhombic crystal structures of the samples are confirmed by the room temperature X-ray diffraction. The dependence of the Curie temperature (T_C) and the magnetic entropy change (ΔS_M) on the Ni doping content was investigated. The samples with x = 0 had the first order phase transition, while the samples with x = 0.05 and 0.1 had the second order phase transition. As the concentration of Ni increased, the maximum entropy change (|ΔS_M|_max) decreased gradually, from 2.78 J·kg⁻¹·K⁻¹ (x = 0) to 1.02 J·kg⁻¹·K⁻¹ (x = 0.1), in a magnetic field change of 15 kOe. The measured value of T_C was 185 K, 150 K and 145 K for x = 0, 0.05 and 0.1, respectively. The phase transition temperatures became wider as x increased. It indicates that the Mn-site substitution by Ni may be used to tailor the Curie temperature in La_0.7Ca_0.3Mn_1-xNi_xO₃.

We studied the structural and electrical properties of SrRuO₃ thin films grown on SrTiO₃ (110) substrate. High resolution X-ray diffraction measurement of the grown film showed 1) very sharp peaks for SrRuO₃ film with a very narrow rocking curve with FWHM = 0.045° and 2) coherent growth behavior having the same in-plane lattice constants of the film as those of the substrate. The resisitivity data showed good metallic behavior; ρ = 63 (205) μΩ·cm at 5 (300) K with a residual resistivity ratio of ~3. The observed kink at ρ(T) showed that the ferromagnetic transition temperature was ~10 K higher than that of SrRuO₃ thin film grown on SrTiO₃ (001) substrate. The observed rather lower RRR value could be partially due to a very small amount of Ru vacancy generally observed in SrRuO₃ thin films grown by PLD method and is evident in the larger unit-cell volume compared to that of stoichiometric thin film.

A pulsed ferrite magnetic field generator (FMFG) was designed for the use in the 1000 m long through-theearth (TTE) communication system for mining disaster situations. To miniaturize the TTE system, a ferrite core having 10,000 of permeability was used for the FMFG. Attenuation of the magnetic field intensity from the FMFG (200-turn and 0.18 m diameter) was calculated to be 89.95 dB at 1000 m depth soil having 0.1 S/m of conductivity. This attenuation was lower than 151.13 dB attenuation of 1 kHz electromagnetic wave at the same conditions. Therefore, the magnetic-field was found to be desirable as a signal carrier source for TTE communications as compared to the electromagnetic wave. The designed FMFG generates the magnetic field intensity of 1 × 10⁻¹⁰ Tesla at 1000 m depth. This magnetic field is detectable by compact magnetic sensors such as flux gate or magnetic tunneling junction sensor. Therefore, the miniature FMFG TTE communication system can replace the conventional electromagnetic wave carrier type TTE system and allow reliable signal transmission between rescuer and trapped miners.

In this paper, the 6-switch inverter for the Flux-Reversal Motor (FRM) has been presented and compared to the 4-switch inverter for the FRM, which is more popular in cost effective applications. To analyze the FRM, we adopted the two-dimensional time-stepped voltage source finite element method (FEM) that uses the actual pulse width modulation (PWM) voltage waveforms as the input data. As the FRM characteristic analysis of actual pwm voltage input, the torque ripples and iron losses (eddy current and hysteresis loss) of the FRM can be precisely calculated. With the simulated and experimental results, the performance and limitations of the 4-switch FRM which is the cost effective drive compared to the 6-switch FRM drive are provided in more detail.

Flux linkage of phase windings is a key parameter in determining the behavior of a switched reluctance motor (SRM) [1-8]. Therefore, the accurate prediction of flux linkage at aligned and unaligned rotor positions makes a significant contribution to the design of an SRM and its analytical approach is not straightforward due to nonlinear saturation in flux. Although several different approaches using a finite element analysis (FEA) or a curve-fitting tool have been employed to compute phase flux linkage [2-5], they are not suitable for a simple design procedure because the FEA necessitates a large amount of time in both modeling and solving with complexity for every motor design, and the curve-fitting requires the data of flux linkage from either an experimental test or an FEA simulation. In this paper, phase flux linkage at aligned and unaligned rotor positions is estimated by means of a reluctance network, and the proposed approach is analytically verified in terms of accuracy compared to FEA.

In this paper, design and performance analysis of robust and inexpensive permanent magnet-assisted synchronous reluctance generators (PMa-SynRG) for tactical and commercial generator sets is studied. More specifically, the optimal design approach is investigated for minimizing volume and maximizing performance for the portable generator. In order to find optimized PMa-SynRG, stator winding configurations and rotor structures are analyzed using the lumped parameter model (LPM). After comparisons of stator windings and rotor structure by LPM, the selected stator winding and rotor structure are optimized using a differential evolution strategy (DES). Finally, output performances are verified by finite element analysis (FEA) and experimental tests. This design process is developed for the optimized design of PMa-SynRG to achieve minimum magnet and machine volume as well as maximum efficiency simultaneously.

This paper proposes a sampling-based optimization method for electromagnetic design problems, where design sensitivities are obtained from the elaborate surrogate models based on the universal Kriging method and a local window concept. After inserting additional sequential samples to satisfy the certain convergence criterion, the elaborate surrogate model for each true performance function is generated within a relatively small area, called a hyper-cubic local window, with the center of a nominal design. From Jacobian matrices of the local models, the accurate design sensitivity values at the design point of interest are extracted, and so they make it possible to use deterministic search algorithms for fast search of an optimum in design space. The proposed method is applied to a mathematical problem and a loudspeaker design with constraint functions and is compared with the sensitivity-based optimization adopting the finite difference method.