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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of Magnetics
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Journal DOI :
The Korean Magnetics Society
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Volume & Issues
Volume 16, Issue 4 - Dec 2011
Volume 16, Issue 3 - Sep 2011
Volume 16, Issue 2 - Jun 2011
Volume 16, Issue 1 - Mar 2011
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Magnetic Properties of Ordered L1
: A First Principles Study
Kim, Dong-Yoo ; Hong, Ji-Sang ;
Journal of Magnetics, volume 16, issue 3, 2011, Pages 197~200
DOI : 10.4283/JMAG.2011.16.3.197
Using the full potential linearized augmented plane wave (FLAPW) method, the influences of uniform and tetragonal strains on the magnetic state have been explored for chemically ordered bulk
. The ordered state displays antiferromagnetic
) state but it transitions into antiferromagnetic
) state at about 10% uniform strain. The ferromagnetic (FM) state is observed at 11% uniform strain. For tetragonal strain, it is also seen that the transition from AFM-
depends on the strength and direction of the applied strain. The FM state does not appear in this case. Magnetocrystalline anisotropy (MCA) calculations for tetragonal distortion reveal that the spin reorientation transition occurs. In addition, we find that the direction of magnetization and the magnitude of magnetic anisotropy energy strongly depend on the c/a ratio.
Structural, Magnetic, and Electronic Properties of Fe: A Screened Hybrid Functional Study
Jang, Young-Rok ; Yu, Byung-Deok ;
Journal of Magnetics, volume 16, issue 3, 2011, Pages 201~205
DOI : 10.4283/JMAG.2011.16.3.201
We performed total energy and electronic structure calculations for the basic ground state properties of Fe using the conventional generalized gradient approximation (GGA) and screened hybrid functionals as the form of the exchange-correlation functional. To that end, we calculated structural (equilibrium lattice constants, bulk moduli, and cohesive energies) and electronic (magnetic moments and densities of states) properties. Both functional calculations gave the correct ground state, the ferromagnetic bcc phase, in which the structural parameters agreed well with experimental results. However, the description of the cohesive energies and magnetic moments at the ground state exhibited different behavior from each other: the unusually small cohesive energy and large magnetic moment were observed in the screened hybrid functional calculations compared to the GGA calculations. The reason for the difference was examined by analyzing the calculated electronic structures.
Optimization of Ferromagnetic Resonance Spectra Measuring Procedure for Accurate Gilbert Damping Parameter in Magnetic Thin Films Using a Vector Network Analyzer
Kim, D.H. ; Kim, H.H. ; You, Chun-Yeol ; Kim, Hyung-Suk ;
Journal of Magnetics, volume 16, issue 3, 2011, Pages 206~210
DOI : 10.4283/JMAG.2011.16.3.206
We optimize a vector network analyzer ferromagnetic resonance (VNA-FMR) measurement system to study spin dynamics and Gilbert damping parameters of thin ferromagnetic films. In order to obtain accurate damping parameters, careful determination of the susceptibility line-width is required. The measured S-parameters are converted into the corresponding susceptibility through a calibration processes. From the line-width measurements, we can successfully extract the saturation magnetizations and Gilbert damping parameters of 5-, 8-, and 10-nm thick
Dynamic Magnetostriction Characteristics of an Fe-Based Nanocrystalline FeCuNbSiB Alloy
Chen, Lei ; Li, Ping ; Wen, Yumei ;
Journal of Magnetics, volume 16, issue 3, 2011, Pages 211~215
DOI : 10.4283/JMAG.2011.16.3.211
The dynamic magnetostriction characteristics of an Fe-based nanocrystalline FeCuNbSiB alloy are investigated as a function of the dc bias magnetic field. The experimental results show that the piezomagnetic coefficient of FeCuNbSiB is about 2.1 times higher than that of Terfenol-D at the low dc magnetic bias
= 46 Oe. Moreover, FeCuNbSiB has a large resonant dynamic strain coefficient at quite low Hdc due to a high mechanical quality factor, which is 3-5 times greater than that of Terfenol-D at the same low
. Based on such magnetostriction characteristics, we fabricate a new type of transducer with FeCuNbSiB/PZT-8/FeCuNbSiB. Its maximum resonant magnetoelectric voltage coefficient achieves ~10 V/Oe. The ME output power reaches 331.8
at an optimum load resistance of 7
under 0.4 Oe ac magnetic field, which is 50 times higher than that of the previous ultrasonic-horn-substrate composite transducer and it decreases the size by nearly 86%. The performance indicate that the FeCuNbSiB/PZT-8/FeCuNbSiB transducer is promising for application in highly efficient magnetoelectric energy conversion.
Ferromagnetic Domain Behaviors in Mn doped ZnO Film
Soundararajan, Devaraj ; Santoyo-Salazar, Jaime ; Ko, Jang-Myoun ; Kim, Ki-Hyeon ;
Journal of Magnetics, volume 16, issue 3, 2011, Pages 216~219
DOI : 10.4283/JMAG.2011.16.3.216
Mn doped ZnO films were prepared on Si (100) substrates using sol-gel method. The prepared films were annealed at
for decomposition and oxidation of the precursors. XRD analysis revealed the presence of ZnMnO hexagonal wurtzite phase along with the presence of small quantity of
secondary phase and poor crystalline nature. The 2D, 3D views of magnetic domains and domain profiles were obtained using magnetic force microscopy at room temperature. Rectangular shaped domains with an average size of 4.16 nm were observed. Magnetic moment measurement as a function of magnetic field was measured using superconducting quantum interference device (SQUID) magnetometry at room temperature. The result showed the ferromagnetic hysteresis loop with a curie temperature higher than 300 K.
Anisotropic Mechanical Properties of Pr(Co,In)
-type Compounds and Their Relation to Texture Formation in Die-upset Magnets
Kwon, H.W. ; Kim, D.H. ; Yu, J.H. ;
Journal of Magnetics, volume 16, issue 3, 2011, Pages 220~224
DOI : 10.4283/JMAG.2011.16.3.220
Die-upset magnets from a mechanically-milled Pr(Co,In)
-type alloy are known to have a peculiar texture; the easy magnetization axis (c-axis) is perpendicular to the pressing direction. This peculiar texture is thought to be linked closely to the anisotropic mechanical properties of Pr(Co,In)
-type hexagonal compounds. The hardness of the Pr(Co,In)
-type crystal was measured using selectively grown grains in an annealed
alloy button, and the crystallographic orientation was determined by observing the magnetic domain image. The hardness (549 VHN) on the plane with a 'cogwheel'-type domain image was significantly higher than that (510 VHN) on the plane with a 'cigar'-type domain image, indicating that the inter-layer bonding force between the (000l) basal planes is stronger than that between the (hki0) planes. This suggests that the most probable slip plane is the (hki0) plane parallel to the c-axis. During die-upsetting of the Pr(Co,In)
-type alloys the deformation proceeds by (hki0) plane slip, and the c-axis rotates to ultimately become oriented perpendicular to the pressing direction. It is proposed that the peculiar texture in the die-upset Pr(Co,In)
-type magnets is probably developed by slip deformation of the (hki0) plane of the Pr(Co,In)
Effect of Isothermal Aging on the Magnetic Properties of 1Cr-0.5Mo Steel
Kim, Min-Gi ; Ryu, K.S. ; Lee, Y.H. ; Park, J.S. ; Kim, C.G. ;
Journal of Magnetics, volume 16, issue 3, 2011, Pages 225~228
DOI : 10.4283/JMAG.2011.16.3.225
Magnetic properties and Rockwell hardness of 1Cr-0.5Mo steel have been investigated as a function of isothermal aging time. Our results showed that coercivity, hysteresis loss and Rockwell hardness in the aged samples decreased as aging time increased. This phenomenon was analyzed using optical microscopy and scanning electron microscopy. A significant diffusion of Cr and Mo atoms formed
carbides, lowering the matrix strength.
carbides partially segregated inside grains, diffused into grain boundaries, and finally resulted in a soft ferrite matrix and a hard grain boundary. The magnetic and mechanical softening of the matrix is likely to govern the properties of the sample more than the hardening of the grain boundary by carbide precipitations.
TMA Study on Phase Evolution During Hydrogen-assisted Disproportionation of Nd-Fe-B Alloy
Kwon, H.W. ; Yu, J.H. ;
Journal of Magnetics, volume 16, issue 3, 2011, Pages 229~233
DOI : 10.4283/JMAG.2011.16.3.229
Phase evolution during the hydrogen-assisted disproportionation of
alloy was investigated mainly by using a magnetic balance-type thermomagnetic analyser (TMA). In order to avoid any undesirable phase change in the course of heating for TMA, a swift TMA technique with very high heating rate (around 2 min to reach
from room temperature) was adopted. The hydrided
alloy started to be disproportionated in hydrogen from around
, and the alloy after the early disproportionation (from 600 to
) has been partially disproportionated. The partially disproportionated alloy consisted of a mixture of
-Fe, and the remaining undisproportionated
-phase. During the subsequent heating to
in hydrogen, two additional phases of
were formed, and the material consisted of a mixture of
-Fe phases. During the subsequent isothermal holding at
for 1 hour, the phase constitution was further changed, and one additional unknown magnetic phase was formed. Eventually, the fully disproportionated
alloy consisted of
-Fe, and one additional unknown magnetic phase.
3 Stage 2 Switch Application for Transcranial Magnetic Stimulation
Ha, Dong-Ho ; Kim, Whi-Young ; Choi, Sun-Seob ;
Journal of Magnetics, volume 16, issue 3, 2011, Pages 234~239
DOI : 10.4283/JMAG.2011.16.3.234
Transcranial magnetic stimulation utilizes the method of controlling applied time and changing pulse by output pulse through power density control for diagnosis purposes. Transcranial magnetic stimulation can also be used in cases where diagnosis and treatment are difficult since output pulse shape can be changed. As intensity, pulse range, and pulse shape of the stimulation pulse must be changed according to lesion, the existing sine wave-shaped stimulation treatment pulse poses limitations in achieving various treatments and diagnosis. This study actualized a new method of transcranial magnetic stimulation that applies a 3 Stage 2 Switch( power semiconductor 2EA) for controlling pulse repetition rate by achieving numerous switching control of stimulation coil. Intensity, pulse range, and pulse shape of output can be freely changed to transform various treatment pulses in order to overcome limitations in stimulation treatment presented by the previous sine wave pulse shape. The method of freely changing pulse range by using 3 Stage 2 Switch discharge method is proposed. Pulse shape, composed of various pulse ranges, was created by grafting PFN (Pulsed Forming Network) through AVR AT80S8535 one-chip microprocessor technology, and application in transcranial magnetic stimulation was achieved to study the output characteristics of stimulation treatment pulse according to delaying time of the trigger signal applied in section switch.
A Hybrid ON/OFF Method for Fast Solution of Electromagnetic Inverse Problems Based on Topological Sensitivity
Kim, Dong-Hun ; Byun, Jin-Kyu ;
Journal of Magnetics, volume 16, issue 3, 2011, Pages 240~245
DOI : 10.4283/JMAG.2011.16.3.240
A new hybrid ON/OFF method is presented for the fast solution of electromagnetic inverse problems in high frequency domains. The proposed method utilizes both topological sensitivity (TS) and material sensitivity (MS) to update material properties in unit design cells. MS provides smooth design space and stable convergence, while TS enables sudden changes of material distribution when MS slows down. This combination of two sensitivities enables a reduction in total computation time. The TS and MS analyses are based on a variational approach and an adjoint variable method (AVM), which permits direct calculation of both sensitivity values from field solutions of the primary and adjoint systems. Investigation of the formulations of TS and MS reveals that they have similar forms, and implementation of the hybrid ON/OFF method that uses both sensitivities can be achieved by one optimization module. The proposed method is applied to dielectric material reconstruction problems, and the results show the feasibility and effectiveness of the method.
Full Wave Cockroft Walton Application for Transcranial Magnetic Stimulation
Choi, Sun-Seob ; Kim, Whi-Young ;
Journal of Magnetics, volume 16, issue 3, 2011, Pages 246~252
DOI : 10.4283/JMAG.2011.16.3.246
A high-voltage power supply has been built for activation of the brain via stimulation using a Full Wave Cockroft-Walton Circuit (FWCW). A resonant half-bridge inverter was applied (with half plus/half minus DC voltage) through a bidirectional power transistor to a magnetic stimulation device with the capability of producing a variety of pulse forms. The energy obtained from the previous stage runs the transformer and FW-CW, and the current pulse coming from the pulse-forming circuit is transmitted to a stimulation coil device. In addition, the residual energy in each circuit will again generate stimulation pulses through the transformer. In particular, the bidirectional device modifies the control mode of the stimulation coil to which the current that exceeds the rated current is applied, consequently controlling the output voltage as a constant current mode. Since a serial resonant half-bridge has less switching loss and is able to reduce parasitic capacitance, a device, which can simultaneously change the charging voltage of the energy-storage condenser and the pulse repetition rate, could be implemented. Image processing of the brain activity was implemented using a graphical user interface (GUI) through a data mining technique (data mining) after measuring the vital signs separated from the frequencies of EEG and ECG spectra obtained from the pulse stimulation using a 90S8535 chip (AMTEL Corporation).
The Effects of Pulsed Elctromagnetic Fields on Expression of Neurotrophic Factors after Spinal Cord Hemisection in Rats
Kang, Ji-Hyuk ; Park, Sang-Young ; Lee, Yun-Seob ;
Journal of Magnetics, volume 16, issue 3, 2011, Pages 253~258
DOI : 10.4283/JMAG.2011.16.3.253
The purpose of this study was to identify the effect of pulsed electromagnetic fields on the expression of neurotrophic factors after spinal cord injury. Sprague-Dawley male rats were given a spinal cord hemisection and randomly divided into 2 groups, the control and experimental groups. The experimental group was administered a fifteen minutes session of pulsed electromagnetic field once a day, five days a week. In order to observe the effect of these pulsed electromagnetic fields, this study observed the BDNF expression in the rat's lumbar spinal cord and the H&E staining in the gastrocnemius at 3, 7, 14, 21 days group after spinal cord hemisection. The results of this showed that the immunoreactivity of the BDNF in the rat's spinal cord gradually increased in each group. At 21 days, there is a significant difference between the control and experimental groups. The morphological shape of the gastrocnemius was gradually changed from 3days to 21days, and the gastrocnemius at 21 days was significantly degraded. However, the experimental group showed a slightly more organized gastrocnemius than the control group at 21days. The Results of this study suggest that pulsed electromagnetic field application decreases the degeneration of a rat's gastrocnemius morphology, and increases the immunoreactivity of the BDNF in the rat's spinal cord after spinal cord hemisection.
The Effect of Magnetic Field Direction on the EEG and PPG Obtained from Pulsed Magnetic Stimulus at Acupoint PC9
Kim, Sun-Wook ; Lee, Jin-Yong ; Lee, Hyun-Sook ;
Journal of Magnetics, volume 16, issue 3, 2011, Pages 259~262
DOI : 10.4283/JMAG.2011.16.3.259
Compared to acupuncture, the pulsed magnetic field (PMF) stimulus is a useful tool for treatment of many physical conditions and health maintenance due to its advantages as a noninvasive and nontoxic medical treatment. The purpose of this study was to investigate the effect of PMF stimulus direction at PC9 on the alpha activity of electroencephalogram (EEG) and vascular aging calculated from photoplethysmograph (PPG). It can be concluded that the direction of PMF stimulus affects the increase of alpha activity of EEG and PPG, indicating the vascular stiffness and the sclerosis level of blood vessels weakly relevant to the direction of PMF stimulus.
Considerations on Improvement of Moving Properties for Magnetic Actuator Capable of Movement in Pipe
Izumikawa, Tomohiro ; Yaguchi, Hiroyuki ;
Journal of Magnetics, volume 16, issue 3, 2011, Pages 263~267
DOI : 10.4283/JMAG.2011.16.3.263
The present paper proposes a novel cableless magnetic actuator with a new propulsion module that exhibits a very high thrusting force. This actuator contains an electrical inverter that directly transforms DC from button batteries into AC. The electrical DC-AC inverter incorporates a mass-spring system, a reed switch, and a curved permanent magnet that switches under an electromagnetic force. The actuator is moved by the inertial force of the mass-spring system due to mechanical resonance energy. The experimental results show that the actuator is able to move upward at a speed of 33 mm/s when using 10 button batteries when pulling a 10 g load mass. This cableless magnetic actuator has several possible applications, including narrow-pipe inspection and maintenance.
Optimal Shape Design of Magnetic Actuators for Magnetic and Dynamic Characteristic Improvement
Yoo, Jeong-Hoon ; Jung, Jae-Yeob ; Hong, Hyeok-Soo ;
Journal of Magnetics, volume 16, issue 3, 2011, Pages 268~270
DOI : 10.4283/JMAG.2011.16.3.268
This study introduces a new topology optimization scheme combing the genetic algorithm (GA) with the on/off sensitivity method for the magnetic actuator core and the armature design. The design process intended to maximize the first eigen-frequency of the armature part and the magnetic actuating force acting on the armature simultaneously. GA based optimal design was carried out to obtain the initial structure and the modified on/off sensitivity method was succeeded to accelerate the design process. Final results show tens of percent improvement in actuating force as well as the first eigen-frequency of the armature.
A High-sensitivity Passive Magnetic Transducer Based on PZT Plates and a Fe-Ni Fork Substrate
Li, Ping ; Wen, Yumei ; Jia, Chaobo ; Li, Xinshen ;
Journal of Magnetics, volume 16, issue 3, 2011, Pages 271~275
DOI : 10.4283/JMAG.2011.16.3.271
This paper proposes a magnetoelectric (ME) composite transducer structure consisting of a magnetostrictive H-type Fe-Ni fork substrate and piezoelectric PZT plates. The fork composite structure has a higher ME voltage coefficient compared to other ME composite structures due to the higher quality (Q) factor. The ME sensitivity of the fork structure reaches 12 V/Oe (i.e., 150 V/cm Oe). The fork composite with two PZT plates electrically connected in series exhibits over 5 times higher ME voltage coefficient than the output of the rectangle structure in the same size. The experiment shows the composite of a Fe-Ni fork substrate and PZT plates has a significantly enhanced ME voltage coefficient and a higher ME sensitivity relative to the prior sandwiched composite laminates. By the use of a lock-in amplifier with 10 nV resolution, this transducer can detect a weak magnetic field of less than
T. This transducer can also be designed for a magnetoelectric energy harvester due to its passive high-efficiency ME energy conversion.
Eddy Current Testing for Radiator Tubes Surrounded by Cooling Fins
Nagata, Shoichiro ; Tsubusa, Yoshiaki ; Enokizono, Masato ;
Journal of Magnetics, volume 16, issue 3, 2011, Pages 276~280
DOI : 10.4283/JMAG.2011.16.3.276
This paper presents a non-destructive evaluation study on a radiator with cooling fins as a complex shaped specimen. Radiator structures are used in various heat exchangers, such as automobiles, air conditioners and refrigerators. An eddy current testing method, namely multi-frequency excitation and spectrogram method (MFES), was employed to detect a defect on the radiator tube surrounded by cooling fins. Overall, experimental results suggested that the influence of cooling fin is not as noticeable as that of the defect signals.
A Study on the Reduction of Cogging Force of Stationary Discontinuous Armature Linear Synchronous Motor Using Auxiliary Teeth
Kim, Yong-Jae ; Lee, Kyu-Myung ; Watada, Masaya ;
Journal of Magnetics, volume 16, issue 3, 2011, Pages 281~287
DOI : 10.4283/JMAG.2011.16.3.281
The stationary discontinuous armatures that are used in permanent magnet linear synchronous motors (PM-LSMs) have been proposed as a driving source for transportation systems. However, the stationary discontinuous armature PM-LSM contains the outlet edges which always exist as a result of the discontinuous arrangement of the armature. For this reason, the high alteration of the outlet edge cogging force produced between the armature's core and the mover's permanent magnet when a mover passes the boundary between the armature's installation part and non-installation part has been indicated as a problem. Therefore, we have examined the outlet edge cogging force by installing the auxiliary teeth at the armature's outlet edge in order to minimize the outlet edge cogging force generated when the armature is arranged discontinuously. Moreover, we obtained the calculation by analyzing the shape of the auxiliary teeth in which the outlet edge cogging force is minimized the most.
Minimization of Cogging Force in a Stationary Discontinuous Armature Linear Permanent Magnet Motor at the Outlet Edge
Kim, Yong-Jae ; Jung, Sang-Yong ;
Journal of Magnetics, volume 16, issue 3, 2011, Pages 288~293
DOI : 10.4283/JMAG.2011.16.3.288
Generally, the discontinuous armature permanent magnet linear synchronous motor (PM-LSM) is composed by the stator block (accelerator, re-accelerator, and decelerator) and the free running section. However, the stationary discontinuous armature design involves the velocity variation of the mover during drive when the armature's non-installation part changes over to installation part as a result of the outlet edge of the armature. Therefore, we considered deforming the shape of the outlet edge at the armature and apply skew on the permanent magnet by displacing the two magnet segments of each pole. This paper presents the results of a three-dimensional (3-D) numerical analysis with a finite element method (FEM) of the force exerted by the outlet edge.
Effect of Die-upset Process on Magnetic Properties and Deformation Behavior of Nanostructured Nd-Fe-B Magnets
Zhao, R. ; Zhang, W.C. ; Li, J.J. ; Wang, H.J. ; Zhu, M.G. ; Li, W. ;
Journal of Magnetics, volume 16, issue 3, 2011, Pages 294~299
DOI : 10.4283/JMAG.2011.16.3.294
Nd-Fe-B high performance magnets were prepared by die-upset forging. The effects of the deformation parameters on magnetic properties and flow stress were studied. Deformation temperatures in the range of
enable to achieve an effective anisotropy and temperature
proves to be suitable for deformation of Nd-Fe-B magnets. The amount of c-axis alignment along the press direction seems to depend on the amount of deformation and a saturation behavior is shown at deformation ratio of 75%. Magnetic properties are also related to strain rate, and maximum energy product is attained at an optimum strain rate of
. By analyzing the relationship of stress and strain at different deformation temperature during die-upset forging process, deformation behavior of Nd-Fe-B magnets was studied and parameters for describing plastic deformation were obtained. Nd-rich boundary liquid phase, which is additionally decreasing the flow stress during deformation, is supposed to play the role of diffusion path and enhance the diffusion rate.
Effect of Hot-compaction Temperature on the Magnetic Properties of Anisotropic Nanocrystalline Magnets
Li, W. ; Wang, H.J. ; Lin, M. ; Lai, B. ; Li, D. ; Pan, W. ;
Journal of Magnetics, volume 16, issue 3, 2011, Pages 300~303
DOI : 10.4283/JMAG.2011.16.3.300
The effect of the hot-compaction temperature on the microstructure and magnetic properties of anisotropic nanocrystalline magnets was investigated. The hot-compaction temperature was found to impact both the magnetic properties and the microstructure of die-upset magnets. The remanence of the isotropic precursor increases slightly with the improved hot-compaction temperature, and the grains start to grow on the flake boundary at higher hot-compaction temperatures. After hot deformation, it was found that the change in the magnetic properties was the inverse of that observed with the hot-compaction temperature. Microstructural investigation showed that die-upset magnets inherit the microstructural characteristics of their precursor. For the die-upset magnets, hot pressed at low temperature, scarcely any abnormal grain growth on the flake boundary can be seen. For those hot pressed at higher temperatures, however, layers with large equiaxed grains could be observed, which accounted for the poor alignment during the hot deformation, and thus the poor magnetic properties.
Effect of Microstructure on the Corrosion Resistance of Nd-Fe-B Permanent Magnets
Li, Jiajie ; Li, Wei ; Li, Anhua ; Zhao, Rui ; Lai, Bin ; Zhu, Minggang ;
Journal of Magnetics, volume 16, issue 3, 2011, Pages 304~307
DOI : 10.4283/JMAG.2011.16.3.304
High performance Nd-Fe-B magnets can be manufactured by both sintering and hot deformation. The corrosion behaviors of the magnets prepared by the two processes were compared. Effect of microstructure on the corrosion resistance of Nd-Fe-B magnets was also investigated. A neutral salt spray test (NSS) was performed for the different-processed magnets. The weight losses of the samples after the corrosion test were measured. The corrosion microstructures were observed using a scanning electron microscope. It shows that the corrosion resistance of hot deformed magnets is much better than that of the sintered ones because the grain size and the distribution of Nd-rich phases of the hot deformed magnets are much finer and more uniform than those of the sintered ones. The different microstructure between the sintered and the hot deformed magnets causes the different corrosion behavior.
Effect of Nucleation and Growth Dynamics on Saturation Magnetization of Chemically Synthesized Fe Nanoparticles
Ogawa, T. ; Seto, K. ; Hasegawa, D. ; Yang, H.T. ; Kura, H. ; Doi, M. ; Takahashi, M. ;
Journal of Magnetics, volume 16, issue 3, 2011, Pages 308~311
DOI : 10.4283/JMAG.2011.16.3.308
In order to obtain mono-dispersed Fe NPs with high saturation magnetization, quantitative analysis method to investigate the growth dynamics of the Fe NPs synthesized by a conventional thermal decomposition method has been developed. As a result, fast nucleation process promotes formation of ~4 nm of initial nucleus with a non-equilibrium phase, resulting in low saturation magnetization. And slow particle growth with atomic-scaled surface precipitation mode (< 100 atoms/(
)) can form the growth layer on the surface of initial nucleus with high saturation magnetization (~190 emu/
) as an equilibrium a phase of Fe. Therefore, higher stabilization of small initial nucleus generated just after the injection of
should be one of the key issues to achieve much higher
of Fe NPs.
A Study on Prototype Hybrid (LTS/HTS) Magnet for NMR Application
Choi, Suk-Jin ; Hwang, Young-Jin ; Ko, Tae-Kuk ;
Journal of Magnetics, volume 16, issue 3, 2011, Pages 312~317
DOI : 10.4283/JMAG.2011.16.3.312
NMR over 1 GHz (23.5 T) level has difficulties in design and fabrication with only low temperature superconducting (LTS) wire because of its material characteristics such as the decay of critical current under the magnetic field. Because High temperature superconducting (HTS) tape has a good performance under the extremely high magnetic field, it has been developed for high-field magnet over 23.5 T. In this paper, the LTS magnet was made for applying magnetic fields externally and the HTS coil was designed and fabricated. The electromagnetic field analysis has been done with respect to the structure and the operating current of the LTS and HTS coil. Considering to the field homogeneity and the center field, the design parameters which is suitable for the HTS coil were found. The HTS insert coil was impregnated with epoxy resin in order to prevent the movement of winding during energizing the magnet. The hybrid magnet (LTS/HTS) magnet was fabricated and tested based on the design parameters. The experimental result shows that the LTS background magnet and the HTS insert coil can be operated stable beyond 220 A and 210 A. The final value 4.32 T at the center was acquired.
Fabrication and Magnetic Properties of A New Fe-based Amorphous Compound Powder Cores
Xiangyue, Wang ; Feng, Guo ; Caowei, Lu ; Zhichao, Lu ; Deren, Li ; Shaoxiong, Zhou ;
Journal of Magnetics, volume 16, issue 3, 2011, Pages 318~321
DOI : 10.4283/JMAG.2011.16.3.318
A new Fe-based amorphous compound powder was prepared from Fe-Si-B amorphous powder by crushing amorphous ribbons as the first magnetic component and Fe-Cr-Mo metallic glassy powder by water atomization as the second magnetic component. Subsequently by adding organic and inorganic binders to the compound powder and cold pressing, the new Fe-based amorphous compound powder cores were fabricated. This new Fe-based amorphous compound powder cores combine the superior DC-Bias properties and the excellent core loss. The core loss of 500 kW/
= 0.1T and f = 100 kHz was obtained When the mass ratio of FeSiB/FeCrMo equals 3:2, and meanwhile the DC-bias properties of the new Fe-based amorphous compound powder cores just decreased by 10% compared with that of the FeSiB powder cores. In addition, with the increasing of the content of the FeCrMo metallic glassy powder, the core loss tends to decrease.