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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 18, Issue 4 - Dec 2013
Volume 18, Issue 3 - Sep 2013
Volume 18, Issue 2 - Jun 2013
Volume 18, Issue 1 - Mar 2013
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Half-metallic and Magnetic Properties of (001) Surfaces of KCaN
Compound in full-Heusler Structure
Bialek, Beata ; Lee, Jae Il ;
Journal of Magnetics, volume 18, issue 4, 2013, Pages 375~379
DOI : 10.4283/JMAG.2013.18.4.375
The electronic and the magnetic properties of (001) surface of
half-metallic compound with full-Heusler structure are studied with the use of a full-potential linearized augmented plane wave method. Two possible terminations of the surface are considered and only the one with N atoms in the topmost layer is found to retain the half-metallic properties of the bulk. The magnetic properties of N-terminated surface are enhanced compared with the properties of the bulk. The calculated magnetic moments on the N atoms in the
in the bulk and 1.90
at the surface. The subsurface metal atoms are also slightly polarized. In the surface terminated with metal atoms, not only the half-metallicity is destroyed, but also the magnetic properties of the system are weakened.
Metastable Vortex State of Perpendicular Magnetic Anisotropy Free Layer in Spin Transfer Torque Magnetic Tunneling Junctions
You, Chun-Yeol ; Kim, Hyungsuk ;
Journal of Magnetics, volume 18, issue 4, 2013, Pages 380~385
DOI : 10.4283/JMAG.2013.18.4.380
We find a metastable vortex state of the perpendicular magnetic anisotropy free layer in spin transfer torque magnetic tunneling junctions by using micromagnetic simulations. The metastable vortex state does not exist in a single layer, and it is only found in the trilayer structure with the perpendicular magnetic anisotropy polarizer layer. It is revealed that the physical origin is the non-uniform stray field from the polarizer layer.
Magnetic and Magnetocaloric Properties of Perovskite Pr
Hua, Sihao ; Zhang, Pengyue ; Yang, Hangfu ; Zhang, Suyin ; Ge, Hongliang ;
Journal of Magnetics, volume 18, issue 4, 2013, Pages 386~390
DOI : 10.4283/JMAG.2013.18.4.386
This paper studies the effects of A-site substitution by barium on the magnetic and magnetocaloric properties of
(x = 0, 0.04, 0.08 and 0.1). The tetragonal crystal structures of the samples are confirmed by room temperature X-ray diffraction. The dependence of the Curie temperature (
) and the magnetic entropy change (
) on the Ba doping content has been investigated. The samples of all doping contents undergo the second order phase transition. As the concentration of Ba increased, the maximum entropy change (
) increased gradually, from 1.15 J
(x = 0) to 1.36 J
(x = 0.1), in a magnetic field change of 1.5 T. The measured value of
is 265 K, 275 K, 260 K and 250 K for x = 0, 0.04, 0.08 and 0.1, respectively. If combining these samples for magnetic refrigeration, the temperature range of ~220 K and 290 K, where |
|max is stable at ~1.27 J
and RCP = 88.9
= 1.5 T.
compounds, are expected to be suitable for magnetic-refrigeration application due to these magnetic properties.
Effect of Copper Substitution on Structural and Magnetic Properties of NiZn Ferrite Nanopowders
Niyaifar, Mohammad ; Shalilian, Hoda ; Hasanpour, Ahmad ; Mohammadpour, Hory ;
Journal of Magnetics, volume 18, issue 4, 2013, Pages 391~394
DOI : 10.4283/JMAG.2013.18.4.391
In this study, nickel-zinc ferrite nanoparticles, with the chemical formula of
(where x = 0.1- 0.6 by step 0.1), were fabricated by the sol-gel method. The effect of copper substitution on the phase formation and crystal structure of the sample was investigated by X-ray diffraction (XRD), thermo-gravimetry (TG), differential thermal analysis (DTA), Fourier transform infrared spectrometry (FT-IR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD result shows that due to the reduction of Zn content,the crystallite size of the sample increased. The results of the vibration sample magnetometer (VSM) exhibit an increase in saturation magnetization value (Ms) for samples with x
0.3 and a linear decrease for samples with x > 0.3. The variation of saturation magnetization and coercivity of the samples were then studied.
Thermal Stability, Mechanical Properties and Magnetic Properties of Fe-based Amorphous Ribbons with the Addition of Mo and Nb
Han, Bo-Kyeong ; Jo, Hye-In ; Lee, Jin Kyu ; Kim, Ki Buem ; Yim, Haein ;
Journal of Magnetics, volume 18, issue 4, 2013, Pages 395~399
DOI : 10.4283/JMAG.2013.18.4.395
The metallic glass ribbons of
(x = 0, 0.3, 0.6, 0.9 at.%) and
(x = 0, 0.3, 0.6, 0.9 at.%) were obtained by melt spinning with 25-30
thickness. The thermal stability, mechanical properties and magnetic properties of Fe-Co-B-Si based systems were investigated. The values of thermal stability were measured using differential scanning calorimetry (DSC), including glass transition temperature (
), crystallization temperature (
) and supercooled liquid region (
). These amorphous ribbons were identified as fully amorphous, using X-ray diffraction (XRD). The mechanical properties of Febased samples were measured by nano-indentation. Magnetic properties of the amorphous ribbons were measured by a vibrating sample magnetometer (VSM). The amorphous ribbons of
(x = 0, 0.3, 0.6, 0.9 at.%) and
(x = 0, 0.3, 0.6, 0.9 at.%) exhibited soft magnetic properties with low coercive force (
) and high saturation magnetization (Ms).
Coercivity Enhancement of Sintered Nd-Fe-B Magnets by Grain Boundary Diffusion with DyH
Liu, W.Q. ; Chang, C. ; Yue, M. ; Yang, J.S. ; Zhang, D.T. ; Liu, Y.Q. ; Zhang, J.X. ; Yi, X.F. ; Chen, J.W. ;
Journal of Magnetics, volume 18, issue 4, 2013, Pages 400~404
DOI : 10.4283/JMAG.2013.18.4.400
Grain boundary diffusion technique with
nanoparticles was applied to fabricate Dy-less sintered Nd-Fe-B permanent magnets with high coercivity. The magnetic properties and microstructure of magnets were systematically studied. The coercivity and remanence of grain boundary diffusion magnet were improved by 60% and reduced by 7% compared with those of the original magnet, respectively. Meanwhile, both the remanence temperature coefficient (
) and the coercivity temperature coefficient (
) of the magnets were improved after diffusion treatment. Investigation shows that Dy is preferentially enriched as (Nd, Dy)
phase in the surface region of the
matrix grains indicated by the remarkable enhancement of the magneto-crystalline anisotropy field of the magnet. As a result, the magnet diffused with a small amount of Dy nanoparticles possesses enhanced coercivity without remarkably sacrificing its magnetization.
The Effect of Cr doping on the Magnetic and Magnetocaloric Properties of MnCoGe Alloys
Emre, S. Yuce ;
Journal of Magnetics, volume 18, issue 4, 2013, Pages 405~411
DOI : 10.4283/JMAG.2013.18.4.405
The structural, magnetic and magnetocaloric properties of
(x=0.05-0.125) have been investigated by using electron microscopy, x-ray diffraction, calorimetric and magnetic measurements. In this study, our aim is to justify the magnetocaloric effect by tuning the structural and magnetic transition temperature with Cr doping on CoMnGe pure system. The substitution of Cr for Mn leads to a decrease of both structural and magnetic transition temperatures. However, structural and magnetic transition temperatures do not close to each other. From magnetization measurement, we calculate that isothermal entropy change associated with magnetic transition can be as high as 3.82 J
at 302 K in a field of 7 T. Meanwhile, structural phase transition contribution to isothermal entropy change is calculated as 5.85 J
at 322 K for 7 T.
Effects of Annealing Pressures on the Ordering and Microstructures of FePt:Ag Nanocomposite Films
Li, Xiaohong ; Feng, Zhaodi ; Li, Yang ; Song, Wenpeng ; Zhang, Qian ; Liu, Baoting ;
Journal of Magnetics, volume 18, issue 4, 2013, Pages 412~416
DOI : 10.4283/JMAG.2013.18.4.412
FePt:Ag (100 nm) nanocomposite thin films were prepared on naturally-oxidized Si substrates by dc magnetron sputtering at room temperature. X-ray diffraction (XRD) and transmission electron microscopy (TEM) are used to investigate the effects of annealing pressures on the ordering processes and microstructures of these films. The average sizes for the
ordered domains and the FePt grains are reduced to d = 9 nm and D = 13 nm from d = 19 nm and D = 34 nm, respectively, when the annealing pressure is enhanced to 0.6 GPa from room pressure at 873 K. Furthermore, the size distribution is improved into a narrow range. With increasing pressure, the coercivity of
-FePt:Ag thin films decreases from 15.1 to 7.6 kOe. In the present study, the effects of high pressure on the
ordering processes and microstructures of FePt:Ag nanocomposite films were discussed.
Current Density and Thickness Effects on Magnetic Properties of Electrodeposited CoPt Magnetic Films
Kim, Hyeon Soo ; Jeong, Soon Young ; Suh, Su Jeong ;
Journal of Magnetics, volume 18, issue 4, 2013, Pages 417~421
DOI : 10.4283/JMAG.2013.18.4.417
The dominant magnetization reversal behavior of electrodeposited CoPt samples with various thicknesses deposited at different current densities was the domain wall motion by means of wall pinning. The magnetic interaction mechanism was dipolar interaction for all samples. The dipolar interaction strength was significantly affected by the sample thickness rather than by the current density, while the magnetic properties were closely related to the current density.
Effects of NEX on SNR and Artifacts in Parallel MR Images Acquired using Reference Scan
Heo, Yeong-Cheol ; Lee, Hae-Kag ; Cho, Jae-Hwan ;
Journal of Magnetics, volume 18, issue 4, 2013, Pages 422~427
DOI : 10.4283/JMAG.2013.18.4.422
The aim of this study was to investigate effects of the number of acquisitions (NEX) on signal-to-noise (SNR) and artifacts in SENSE parallel imaging of magnetic resonance imaging (MRI). 3.0T MR System, 8 Channel sensitivity encoding (SENSE) head coils were used along with an in-vivo phantom. Reference sequence of 3D fast field echo (FFE) was consisted of NEX values of 2, 4, 6, 8, 10 and 12. The T2 turbo spin echo (TSE) sequence used for exams achieved SENSE factors of 1.2, 1.5, 1.8, 2.0, 2.2, 2.5, 2.8, 3.0, 3.2, 3.5, 3.8 and 4.0. Exams were conducted five times for each SENSE factor to measure signal intensity of the object, the posterior phase-encode direction and frequency direction. And SNR was calculated using mean values. SENSE artifacts were identified as background signal intensity in the phase-encoded direction using MRIcro. It was found that SNR increased but SENSE artifacts reduced with NEX of 4, 8 and 12 when the NEX increased in reference scan. It is therefore concluded that image quality can be improved with NEX of 4, 8 and 12 for reference scanning.
Impedance Matching of Electrically Small Antenna with Ni-Zn Ferrite Film
Lee, Jaejin ; Hong, Yang-Ki ; Lee, Woncheol ; Park, Jihoon ;
Journal of Magnetics, volume 18, issue 4, 2013, Pages 428~431
DOI : 10.4283/JMAG.2013.18.4.428
We demonstrate that a partial loading of
(Ni-Zn ferrite) film remarkably improves impedance matching of electrically small
) hexaferrite antenna. A 3
thick Ni-Zn ferrite film was deposited on a silicon wafer by the electrophoresis deposition process and post-annealed at
. The fabricated Ni-Zn ferrite film has saturation magnetization of
and coercivity of 89 Oe. A partial loading of the Ni-Zn ferrite film on the
hexaferrite helical antenna increases antenna return loss to 24.7 dB from 9.0 dB of the
antenna. Experimental results show that impedance matching and maximum input power transmission to the antenna without additional matching elements can be realized, while keeping almost the same size as the
Gimballing Flywheel and its Novel Reluctance Force-type Magnetic Bearing with Low Eddy Loss and Slight Tilting Torque
Tang, Jiqiang ; Wang, Chun'e ; Xiang, Biao ;
Journal of Magnetics, volume 18, issue 4, 2013, Pages 432~442
DOI : 10.4283/JMAG.2013.18.4.432
For magnetically suspended flywheel (MSFW) with gimballing capability, demerits of Lorentz force-type magnetic bearings and common reluctance force-type magnetic bearings are analyzed, a novel reluctance forcetype magnetic bearing (RFMB) including radial and axial magnetic bearing units with 4 separate biased permanent magnets and two conical stators is presented. By equivalent magnetic circuits' method, its magnetic properties are analyzed. To reduce the eddy loss, it was designed as radial poles with shoes and its rotor made of Iron-based amorphousness. Although the uniformity of magnetic flux density in the conical air gap determines mainly the additional tilting torque, the maximum additional tilting torques is 0.05Nm and the rotor tilting has no influence on its forces when the rotor tilts or the maximum changes does not exceed 14% when the rotor drifts and tilts simultaneously. The MSFW with this RFMB can meet the maneuvering requirement of spacecraft theoretically.
Research on Forces and Dynamics of Maglev Wind Turbine Generator
Wang, Nianxian ; Hu, Yefa ; Wu, Huachun ; Zhang, Jinguang ; Song, Chunsheng ;
Journal of Magnetics, volume 18, issue 4, 2013, Pages 443~453
DOI : 10.4283/JMAG.2013.18.4.443
Maglev wind turbine generator (MWTG) technology has been widely studied due to its low loss, low maintenance cost, and high reliability. However, the dynamics of the magnetic bearing system differ fromthe those of the traditional mechanical bearing system. A horizontal axial MWTG supported with a permanent magnetic bearing is designed in this research and the radial forces and the natural frequencies of the rotor system are studied. The results show that the generatorhas a cyclical magnetic forceand an unreasonable bearing stiffness may mean that the rotor system needs to work in the resonance region; the bearing stiffness is the key factor to avoid this problem. This is the main rule of the bearing stiffness design in the MWTG, and this rule can also be used in other maglev permanent magnet motors.
Optimal Angle Error Reduction of Magnetic Position Sensor by 3D Finite Element Method
Kim, Ki-Chan ;
Journal of Magnetics, volume 18, issue 4, 2013, Pages 454~459
DOI : 10.4283/JMAG.2013.18.4.454
This paper deals with an optimal angle error reduction method of magnetic position sensor using hall effect elements. The angle detection simulation for the magnetic position sensor is performed by 3 dimensional finite element method and Taguchi method, one of the design of experiments. The magnetic position sensor is required to generate ideal sine and cosine waveforms from its hall effect elements according to rotation angle for precise angle information. However, the output signals are easy to include harmonics due to uneven magnetic field distribution from permanent magnet in the air-gap in the vicinity of hall effect elements. For the Taguchi method, three design parameters related to position of hall effect elements and shape of back yoke are selected. The characteristics of optimal magnetic position sensor are compared with those of original one in terms of simulation as well as experiment. Finally, the performances of the motor adopting original model and optimal model are represented for the purpose of verification of motor performance due to signals from magnetic position sensor.
Permanent Magnet Motor Design for Turrets with Large Diameters
Lee, Ji-Young ; Joo, Dae-Suk ; Hong, Do-Kwan ; Chung, Shi-Uk ; Woo, Byung-Chul ; Koo, Dae-Hyun ;
Journal of Magnetics, volume 18, issue 4, 2013, Pages 460~465
DOI : 10.4283/JMAG.2013.18.4.460
This paper deals with an approach for the initial design of a permanent magnet motor for turrets with large diameters. The proposed design techniques are introduced as three stages. The first is the selection of a pole-slot combination, the second is the selection of the rotor topology, and the last is choosing the outermost dimensions. In every stage, a useful technique is described with considerations for effective fabrication and motor performance, and magnetic field computation is performed using the finite element method.
Shorted Turn in the Hybrid Magnet Engine Valve Actuator for Enhanced Dynamic Performance
Yi, Hwa Cho ; Hwang, Ki Il ; Kim, Jihun ; Kim, Jin Ho ;
Journal of Magnetics, volume 18, issue 4, 2013, Pages 466~472
DOI : 10.4283/JMAG.2013.18.4.466
This paper presents a new design of the hybrid magnet engine valve actuator using the shorted turn for enhanced dynamic performance. The quick response of coil electric current is the most important factor that determines the opening and closing performance of the hybrid magnet engine valve. The conventional hybrid magnet engine valve actuator, however, has a delayed initial electric current rising when it is driven by voltage control because of the coil inductance which is a typical characteristic of an electromagnetic coil. A shorted turn is newly placed into the upper yoke of the hybrid magnet engine valve actuator to reduce coil inductance and thus, to hasten the initial electric current rising. We performed a dynamic finite element analysis to demonstrate the improvement of the dynamic characteristics of the hybrid magnet engine valve actuator due to the shorted turn.
Durable and Sustainable Strap Type Electromagnetic Harvester for Tire Pressure Monitoring System
Lee, Soobum ; Kim, Dong-Hun ;
Journal of Magnetics, volume 18, issue 4, 2013, Pages 473~480
DOI : 10.4283/JMAG.2013.18.4.473
A new concept design of electromagnetic energy harvester is proposed for powering a tire pressure monitoring sensor (TPMS). The thin coil strap is attached on the circumferential surface of a rim and a permanent magnet is placed on the brake caliper system. When the wheel rotates, the relative motion between the magnet and the coil generates electrical energy by electromagnetic induction. The generated energy is stored in a storage unit (rechargeable battery, capacitor) and used for TPMS operation and wireless signal transmission. Innovative layered design of the strap is provided for maximizing energy generation. Finite Element Method (FEM) and experiment results on the proposed design are compared to validate the proposed design; further, the method for design improvement is discussed. The proposed design is excellent in terms of durability and sustainability because it utilizes the everlasting rotary motion throughout the vehicle life and does not require material deformation.
Coil Gun Electromagnetic Launcher (EML) System with Multi-stage Electromagnetic Coils
Lee, Su-Jeong ; Kim, Ji-Hun ; Song, Bong Sob ; Kim, Jin Ho ;
Journal of Magnetics, volume 18, issue 4, 2013, Pages 481~486
DOI : 10.4283/JMAG.2013.18.4.481
An electromagnetic launcher (EML) system accelerates and launches a projectile by converting electric energy into kinetic energy. There are two types of EML systems under development: the rail gun and the coil gun. A railgun comprises a pair of parallel conducting rails, along which a sliding armature is accelerated by the electromagnetic effects of a current that flows down one rail, into the armature and then back along the other rail, but the high mechanical friction between the projectile and the rail can damage the projectile. A coil gun launches the projectile by the attractive magnetic force of the electromagnetic coil. A higher projectile muzzle velocity needs multiple stages of electromagnetic coils, which makes the coil gun EML system longer. As a result, the installation cost of a coil gun EML system is very high due to the large installation site needed for the EML. We present a coil gun EML system that has a new structure and arrangement for multiple electromagnetic coils to reduce the length of the system. A mathematical model of the proposed coil gun EML system is developed in order to calculate the magnetic field and forces, and to simulate the muzzle velocity of a projectile by driving and switching the electric current into multiple stages of electromagnetic coils. Using the proposed design, the length of the coil gun EML system is shortened by 31% compared with a conventional coil gun system while satisfying a target projectile muzzle velocity of over 100 m/s.
Development of Wound Rotor Synchronous Motor for Belt-Driven e-Assist System
Lee, Geun-Ho ; Lee, Heon-Hyeong ; Wang, Qi ;
Journal of Magnetics, volume 18, issue 4, 2013, Pages 487~493
DOI : 10.4283/JMAG.2013.18.4.487
The automotive industry is showing widespread interest in belt-driven electric motor-assisted (e-Assist) systems. A belt-driven assist system (BAS) starts and assists the combustion engine in place of the conventional generator. In this study, a water-cooled wound rotor synchronous motor (WRSM) for the e-Assist system was designed and analyzed. The performance of the WRSM was compared with that of an interior permanent magnet synchronous motor (IPMSM). The WRSM efficiency can be improved for the BAS by adjusting the field flux at high speeds. The field current map to obtain the maximum efficiency based on the speed and torque was developed. To control the field flux via field current control in the WRSM, a general H-bridge circuit was added to the WRSM inverter to get the rapid current response in the high-speed region; the characteristics were compared with the chopper circuit. A WRSM developed for the belt-driven e-Assist system and a prototype 115 V power electronic converter to drive the WRSM were tested with a 900 cc combustion engine. The test results showed that the WRSM-type e-Assist system had good characteristics and could successfully start and assist the 900 cc combustion engine.