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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of Magnetics
Journal Basic Information
Journal DOI :
The Korean Magnetics Society
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Volume & Issues
Volume 20, Issue 4 - Dec 2015
Volume 20, Issue 3 - Sep 2015
Volume 20, Issue 2 - Jun 2015
Volume 20, Issue 1 - Mar 2015
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The First-principles Calculations on the Half-metallic Properties of (001) and (110) Surfaces of Zinc-blende YC
Bialek, Beata ; Lee, Jae Il ;
Journal of Magnetics, volume 20, issue 1, 2015, Pages 1~7
DOI : 10.4283/JMAG.2015.20.1.001
We investigated the half-metallicity and magnetism at the (001) and (110) surfaces of YC in zinc-blende structure by using the all-electron full-potential linearized augmented plane wave method within the generalized gradient approximation. From the calculated local density of states, we found that neither (001) nor (110) surface preserves the half-metallicity. While the magnetic moment of Y atom in the YC bulk is
, it is
at the topmost layer of Y-terminated (001) surface. On the contrary, C-terminated (001) YC surface exhibits stronger magnetism than the bulk structure; the calculated magnetic moment on topmost C atom is
, while that of C atom in the bulk structure is
. The magnetic properties of the non-polar (110) YC surface are slightly enhanced as compared with the bulk structure.
Optical Measurement of Magnetic Anisotropy Field in Nanostructured ferromagnetic Thin Films
Whang, Hyun-Seok ; Yun, Sang-Jun ; Moon, Joon ; Choe, Sug-Bong ;
Journal of Magnetics, volume 20, issue 1, 2015, Pages 8~10
DOI : 10.4283/JMAG.2015.20.1.008
The magnetic anisotropy field plays an important role in spin-orbit-torque-induced magnetization dynamics with electric current injection. Here, we propose a magnetometric technique to measure the magnetic anisotropy field in nanostructured ferromagnetic thin films. This technique utilizes a magneto-optical Kerr effect microscope equipped with two-axis electromagnets. By measuring the out-of-plane hysteresis loops and then analyzing their saturated magnetization with respect to the in-plane magnetic field, the magnetic anisotropy field is uniquely quantified within the context of the Stoner-Wohlfarth theory. The present technique can be applied to small nanostructures, enabling in-situ determination of the magnetic anisotropy field of nanodevices.
Monte Carlo Investigation of Spatially Adaptable Magnetic Behavior in Stretchable Uniaxial Ferromagnetic Monolayer Film
Laosiritaworn, Yongyut ; Laosiritaworn, Wimalin ;
Journal of Magnetics, volume 20, issue 1, 2015, Pages 11~20
DOI : 10.4283/JMAG.2015.20.1.011
In this work, Monte Carlo simulation was employed to model the stretchable Ising monolayer film to investigate the effect of the spatial distance variation among magnetic atoms on magnetic behavior of the film. The exchange interaction was considered as functions of initial interatomic distance and the stretched distance (or the strain). Following Bethe-Slater picture, the magnetic exchange interaction took the Lennard-Jones potential-like function. Monte Carlo simulations via the Wolff and Metropolis algorithms were used to update the spin systems, where equilibrium and dynamic magnetic profiles were collected. From the results, the strain was found to have strong influences on magnetic behavior, especially the critical behavior. Specifically, the phase transition point was found to either increase or decrease depending on how the exchange interaction shifts (i.e. towards or away from the maximum value). In addition, empirical functions which predict how the critical temperatures scale with initial interatomic distance and the strain were proposed, which provides qualitatively view how to fine tune the magnetic critical point in monolayer film using the substrate modification induced strain.
Coercivity of Nd-Fe-B-type Fine Particles Prepared from Different Precursor Materials
Kim, K.M. ; Kwon, H.W. ; Lee, J.G. ; Yu, J.H. ;
Journal of Magnetics, volume 20, issue 1, 2015, Pages 21~25
DOI : 10.4283/JMAG.2015.20.1.021
Fine Nd-Fe-B-type particles were prepared by ball milling of different types of Nd-Fe-B precursor materials, such as die-upset magnet, HDDR-treated material, and sintered magnets. Coercivity dependence on the grain and particle size of the powder was investigated. Coercivity of the milled particles was reduced as the particle size decreased, and the extent of coercivity loss was dependent upon the precursor material. Coercivity loss in the finely milled particles was attributed to the surface oxidation. The extent of coercivity loss in the fine particles was closely linked to grain size of the precursor materials. Coercivity loss was more profound for the fine particles with larger grain size. Contrary to the fine particles from the sintered magnets with larger grain size the fine particles (~10 um) from the die-upset magnet and HDDR-treated material with much finer grain size still retained high coercivity (> 10 kOe for die-upset magnet, > 4 kOe for HDDR-treated material).
Effects of Ga Substitution on Crystallographic and Magnetic Properties of Co Ferrites
Chae, Kwang Pyo ; Choi, Won-Ok ; Kang, Byung-Sub ; Lee, Young Bae ;
Journal of Magnetics, volume 20, issue 1, 2015, Pages 26~30
DOI : 10.4283/JMAG.2015.20.1.026
The crystallographic and magnetic properties of gallium-substituted cobalt ferrite (
) were investigated. The new material was synthesized using conventional ceramic methods, with gallium substituted for ferrite in the range of x = 0.0 to 1.0, in steps of 0.2. X-ray diffraction and M
ssbauer spectroscopy were used to confirm the presence of crystallized particles in the
ferrite powders. All of the samples exhibited a single phase with a spinel structure, and the lattice parameters decreased as the gallium content increased. The particle size of the samples also decreased as gallium increased. For
, the M
ssbauer spectra of
could be fitted with two Zeeman sextets, which are the typical spinel ferrite spectra of
with A- and B-sites. However, for
, the M
ssbauer spectra could be fitted with two Zeeman sextets and one doublet. The variation in the M
ssbauer parameters and the absorption area ratio indicated a cation distribution of
, and the magnetic behavior of the samples suggested that the increase in gallium content led to a decrease in the saturation magnetization and in the coercivity.
Hysteresis Loops, Critical Fields and Energy Products for Exchange-spring Hard/soft/hard Trilayers
Chen, B.Z. ; Yan, S. ; Ju, Y.Z. ; Zhao, G.P. ; Zhang, X.C. ; Yue, M. ; Xia, J. ;
Journal of Magnetics, volume 20, issue 1, 2015, Pages 31~39
DOI : 10.4283/JMAG.2015.20.1.031
Macroscopic hysteresis loops and microscopic magnetic moment distributions have been determined by a three-dimensional (3D) model for exchange-coupled Sm-Co/
/Sm-Co trilayers with in-plane collinear easy axes. These results are carefully compared with the popular one-dimensional (1D) micromagnetic models and recent experimental data. It is found that the results obtained from the two methods match very well, especially for the remanence and coercivity, justifying the calculations. Both nucleation and coercive fields decrease monotonically as the soft layer thickness
increases while the largest maximum energy product (roughly 50 MGOe) occurs when the thicknesses of hard and soft layers are 5 nm and 15 nm, respectively. Moreover, the calculated angular distributions in the thickness direction for the magnetic moments are similar. Nevertheless, the calculated nucleation and pinning fields as well as the energy products by 3D OOMMF are systematically smaller than those given by the 1D model, due mainly to the stray fields at the corners of the films. These demagnetization fields help the magnetic moments at the corners to deviate from the previous saturation state and facilitate the nucleation. Such an effect enhances as
increases. When the thicknesses of hard and soft layers are 10 nm and 20 nm, respectively, the pinning field difference is as large as 30%, while the nucleation fields have opposite signs.
Accuracy Analysis of Magnetic Resonance Angiography and Computed Tomography Angiography Using a Flow Experimental Model
Heo, Yeong-Cheol ; Lee, Hae-Kag ; Park, Cheol-Soo ; Cho, Jae-Hwan ;
Journal of Magnetics, volume 20, issue 1, 2015, Pages 40~46
DOI : 10.4283/JMAG.2015.20.1.040
This study investigated the accuracy of magnetic resonance angiography (MRA) and computed tomography angiography (CTA) in terms of reflecting the actual vascular length. Three-dimensional time of flight (3D TOF) MRA, 3D contrast-enhanced (CE) MRA, volume-rendering after CTA and maximum intensity projection were investigated using a flow model phantom with a diameter of 2.11 mm and area of
. 1.5 and 3.0 Tesla devices were used for 3D TOF MRA and 3D CE MRA. CTA was investigated using 16 and 64 channel CT scanners, and the images were transmitted and reconstructed by volume-rendering and maximum intensity projection, followed by conduit length measurement as described above. The smallest 3D TOF MRA measure was
with a flow velocity of 40 cm/s using the 3.0 Tesla apparatus, and
with a velocity of 71.5 cm/s using the 1.5 Tesla apparatus; both images were magnified from the actual measurement of 2.11 mm. The measurement with the 16 channel CT scanner was smaller (
) than the reconstructed image on maximum intensity projection. The images from CTA from examination apparatus and reconstruction technique were all larger than the actual measurement.
Peripheral Blood Flow Velocity and Peripheral Pulse Wave Velocity Measured Using a Clip-type Pulsimeter Equipped with a Permanent Magnet and a Hall Device
Kim, Keun-Ho ; Lee, Sang-Suk ;
Journal of Magnetics, volume 20, issue 1, 2015, Pages 47~51
DOI : 10.4283/JMAG.2015.20.1.047
We measured radial arterial pulse signals using a prototype of a clip-type pulsimeter equipped with a permanent magnet and a Hall device, which produced signals through a voltage-detecting circuit. The systolic peak time and the reflective peak time for a temporally pulsed signal were analyzed for an arbitrary pulse wave at one position of a small permanent magnet. The measured value of the peripheral pulse wave velocity was about 1.25-1.52 m/s, demonstrating the accuracy of this new method. To measure the peripheral blood flow velocity, we simultaneously connected the radial artery pulsimeter to a photoplethysmography meter. The average value of the peripheral blood flow velocity was about 0.27-0.50 m/s.
Therapeutic Efficacy of Low Frequency Transcranial Magnetic Stimulation in Conjunction with Mirror Therapy for Sub-acute Stroke Patients
Cha, Hyun Gyu ; Kim, Myoung-Kwon ;
Journal of Magnetics, volume 20, issue 1, 2015, Pages 52~56
DOI : 10.4283/JMAG.2015.20.1.052
The purpose of the current study was to investigate the effect of repetitive transcranial magnetic stimulation (rTMS) in conjunction with mirror therapy on the balance function of patients with sub-acute stroke hemiparesis. This study was conducted with 36 subjects who were diagnosed with a hemiparesis due to stroke. Participants in the experimental (19 members) and control groups (17 members) received rTMS and sham rTMS during 10 minute sessions each, which were carried out five days per week for four weeks. This was followed by the mirror therapy over 30 minute sessions, which were carried out five days per week for four weeks. Motor recovery was assessed by balance index, dynamic limits of stability, Berg balance scale, and time up go test. The change values of the balance index (
), dynamic limits of stability (
), and time up go test (
score) were significantly higher in the experimental group than in the control group (p < 0.05). At post-test, balance index (
), dynamic limits of stability (
), and time up go test (
) were significantly higher in the experimental group than in the control group (p < 0.05). In the experimental group, significant differences were found in the pre- and post-test scores for the balance index, dynamic limits of stability, Berg balance scale, and time up go test (p < 0.01). In the control group, a significant difference was observed between the pre- and post-test only for the Berg balance scale and time up go test (p < 0.05). These findings demonstrate that the application of 1Hz rTMS in conjunction with mirror therapy can be helpful in improving the balance function of patients with sub-acute stroke hemiparesis, and this may be used as a practical adjunct to routine rehabilitation therapy.
Examination of Efficiency Based on Air Gap and Characteristic Impedance Variations for Magnetic Resonance Coupling Wireless Energy Transfer
Agcal, Ali ; Bekiroglu, Nur ; Ozcira, Selin ;
Journal of Magnetics, volume 20, issue 1, 2015, Pages 57~61
DOI : 10.4283/JMAG.2015.20.1.057
In this paper wireless power transmission system based on magnetic resonance coupling circuit was carried out. With the research objectives based on the mutual coupling model, mathematical expressions of optimal coupling coefficients are examined. Equivalent circuit parameters are calculated by Maxwell software, and the equivalent circuit was solved by Matlab software. The power transfer efficiency of the system was derived by using the electrical parameters of the equivalent circuit. System efficiency was analyzed depending on the different air gap values for various characteristic impedances. Hence, magnetic resonance coupling involves creating a resonance and transferring the power without radiating electromagnetic waves. As the air gap between the coils increased the coupling between the coils were weakened. The impedance of circuit varied as the air gap changed, affecting the power transfer efficiency.
A Magnetic Field Separation Technique for a Scaled Model Ship through an Earth's Magnetic Field Simulator
Chung, Hyun-Ju ; Yang, Chang-Seob ; Jung, Woo-Jin ;
Journal of Magnetics, volume 20, issue 1, 2015, Pages 62~68
DOI : 10.4283/JMAG.2015.20.1.062
This paper presents an experimental technique to accurately separate a permanent magnetic field and an induced one from the total magnetic fields generated by a steel ship, through compensating for the Earth's magnetic field. To achieve this, an Earth's magnetic field simulator was constructed at a non-magnetic laboratory, and the field separation technique was developed, which consisted of five stages. The proposed method was tested with a scaled model ship, and its permanent and induced magnetic fields were successfully extracted from the magnetic field created by the ship. Finally, based on the separated permanent magnetic field data, the permanent magnetization distribution on the hull was predicted by solving an inverse problem. Accordingly, the permanent magnetic fields generated by the ship can easily be calculated at any depth of water.
Design of a Rotary Electromagnetic Actuator with Linear Torque Output for Fast Steering Mirror
Long, Yongjun ; Mo, Jinqiu ; Chen, Xinshu ; Liang, Qinghua ; Shang, Yaguang ; Wang, Shigang ;
Journal of Magnetics, volume 20, issue 1, 2015, Pages 69~78
DOI : 10.4283/JMAG.2015.20.1.069
This paper focuses on the design of a flux-biased rotary electromagnetic actuator with compact structure for fast steering mirror (FSM). The actuator has high force density and its torque output shows linear dependence on both excitation current and rotation angle. Benefiting from a new electromagnetic topology, no additional axial force is generated and an armature with small moment of inertia is achieved. To improve modeling accuracy, the actuator is modeled with flux leakage taken into account. In order to achieve an FSM with good performance, a design methodology is presented. The methodology aims to achieve a balance between torque output, torque density and required coil magnetomotive force. By using the design methodology, the actuator which will be used to drive our FSM is achieved. The finite element simulation results validate the design results, along with the concept design, magnetic analysis and torque output model.
Comparative Study of Armature Reaction Field Analysis for Tubular Linear Machine with Axially Magnetized Single-sided and Double-sided Permanent Magnet Based on Analytical Field Calculations
Shin, Kyung-Hun ; Park, Min-Gyu ; Cho, Han-Wook ; Choi, Jang-Young ;
Journal of Magnetics, volume 20, issue 1, 2015, Pages 79~85
DOI : 10.4283/JMAG.2015.20.1.079
This paper presents a comparative study of a Tubular Linear Machine (TLM) with an Axially Magnetized Single-sided Permanent Magnet (AMSPM) and an Axially Magnetized Double-sided Permanent Magnet (AMDPM) based on analytical field calculations. Using a two-dimensional (2-D) polar coordinate system and a magnetic vector potential, analytical solutions for the flux density produced by the stator windings are derived. This technique is significant for the design and control implementation of electromagnetic machines. The field solution is obtained by solving Maxwell's equations in the simplified boundary value problem consisting of the air gap and coil. These analytical solutions are then used to estimate the self and mutual inductances. Two different types of machine are used to verify the validity of these model simplifications, and the analytical results are compared to results obtained using the finite element method (FEM) and experimental measurement.
Measurements of Magnetic Properties of Electromagnetic Actuator in High-Temperature Environment
Noh, M. ; Gi, M.J. ; Kim, D. ; Park, Y.W. ; Lee, J. ; Kim, J. ;
Journal of Magnetics, volume 20, issue 1, 2015, Pages 86~90
DOI : 10.4283/JMAG.2015.20.1.086
Electromagnetic actuators are versatile and able to meet demanding requirements, such as operation in very low or very high temperatures. When the actuator is used in a high-temperature environment up to
, we need to know how the force-producing capability of the actuator is affected by the operating temperature. Specifically, it is necessary to know the temperature-dependence of magnetic properties that determine the mechanical forces. In this paper, we measure the changes in magnetic properties of SUS410 material in high-temperature environment. We also devise a novel signal processing technique to remove the integration drift. At the field strength of 18,000 A/m, we found that the flux density at
is decreased by 26%, compared to the result at room temperature. Therefore, the actuator must be sized appropriately, if it is to operate in high-temperature settings.
A Design Optimization of Asymmetric Air-gap Structure for Small 3-phase Permanent Magnet SPM BLDC Motor
Kam, Seung-Han ; Jung, Tae-Uk ;
Journal of Magnetics, volume 20, issue 1, 2015, Pages 91~96
DOI : 10.4283/JMAG.2015.20.1.091
As many researchers are relentlessly trying to improve the power generation schemes from the power grid, to meet the constantly increasing electricity demand. In this paper, the results of a finite element analysis are carried out to study on a design optimization of an asymmetric air-gap structure in 3-phase Permanent Magnet Brushless DC Motors. To achieve a high efficiency for a 3-phase PM BLDC motor, the asymmetric air-gap structure is proposed considering the rotation direction of a motor. Generally, a single-phase BLDC motor is applied asymmetric air-gap structure for starting. This is because the asymmetric air-gap structure causes reluctance variation so the motor can utilize reluctance torque toward a rotation direction. In this paper, the asymmetric air-gap is applied to 3-phase BLDC SPM motor so it utilizes reluctance torque with alignment torque. A proposed model is designed by 2-D FE analysis and the results are verified by experimental test.