Magnetic Properties and Cation Distribution of Phosphorous-Doped $Co-{\gamma}-{Fe_2} {O_3}$ Particles

Na, J.G.,Han, D.H. The Korean Magnetics Society 1996 Journal of Magnetics Vol.1 No.1

The effects of additional P-doping on the magnetic properties, thermal stability and cation distribution of Co-doped ${\gamma}-{Fe_2} {O_3}$have been investigated by means of magnetic annealing and measurements with vibration sample magnetometer and torque magnetometer. It is found that the P-doping promotes the coercivity and its magnetic-thermal stability, which may be attributed to increase of the cubic magneto-crystalline anisotropy constant, $K_1$ and the activation energy, E, for cation rearrangement, respectively. The cation distribution of P and Co-substituted iron oxide was calculated from the variation of the saturation magnetization with P-doping on the basis of the Neel model. It was found that the most of P ions in the iron oxides occupied the B-site of spinel lattice.

Study on Magnetic Force Calculation of Spherical Permanent Magnets

Yuyang Zhang,Yonggang Leng,Dan Tan,Jinjun Liu Korean Magnetics Society 2018 Journal of Magnetics Vol.23 No.4

This paper presents three approaches to calculate the interacting magnetic force about spherical permanent magnet, respectively based on magnetic dipole-dipole model, equivalent magnetic charge model and equivalent magnetizing current model. We use all of three models to fully calculate and study the behaviors of lateral and axial forces with respect to the related positions between a pair of spherical magnets. The accuracies of the calculation results are compared with the experimental data. In conclusion, the magnetic dipole-dipole model has the most advantageous accuracy and efficiency for the magnetic force calculation about spherical permanent magnets on account of the particularity of sphere. Our study provides an important criterion for choosing a proper method to calculate magnetic force about spherical permanent magnet.

Study on the Formation and the Magnetic Properties of $Sm_2Fe_{17}N_x$-type Interstitial Material

Kwon, H.W. The Korean Magnetics Society 1996 Journal of Magnetics Vol.1 No.1

In the present study, the $Sm_2Fe_{17}N_x$-type interstitial materials have been prepared by reaction between Nb-free or Nb-containing $Sm_2Fe_{17}$-type alloy and $N_2$ gas. Nitrogenation behaviour of the $Sm_2Fe_{17}N_x$-type material and disproportionation characteristics of the nitrogenated materials have been studied by means of differential thermal analysis (DTA) and thermopiezic analysis (TPA). Magnetic properties of the produced $Sm_2Fe_{17}N_x$-type interstitial materials were characterised in vibrating sample magnetometer (VSM) or thermomagnetic analyser (TMA). Epoxy-bonded or Zn-bonded $Sm_2Fe_{17}N_x$-type magnets were prepared, and their magnetic properties were investigated. It has been found that nitrogenation kinetics of the Sm2Fe17Nx-type alloy is improved significantly by the Nb-substitution for Fe in the alloy. The Nb-substitution is also found to enhance thermal stability of the $Sm_2Fe_{17}N_x$-type interstitial material. Hard magnetic properties of the interstitial materials produced from Nb-free orNb-containing alloy is high enough (intrinsic coercivity : over 7 kOe) for application as bonded permanent magnets. The good hard magnetic properties of the interstitial material are maintained in the epoxy-bonded magnet. Intrinsic coercivity of the Zn-bonded magnets is improved significantly as post-bonding annealing time increases.

Electromagnetic-Thermal Analysis of Axial-Flux Permanent Magnet Eddy Current Couplers with Sub-loop Calculation Method

Dazhi Wang,Di Zheng,Shuo Li,Zhao Li,Bingxue Liang,Yongliang Ni Korean Magnetics Society 2018 Journal of Magnetics Vol.23 No.4

In this paper, a precise electromagnetic–thermal model of axial-flux permanent magnet (PM) eddy current couplers is proposed to calculate the eddy current loss and predict the copper plate node temperature. With subloop calculation method, the quasi 3-D electromagnetic field analytical model is established in cylindrical coordinate. Based on the electromagnetic field analytical model, magnetic field distribution, eddy current losses of PM, copper plate and copper back iron are analyzed under various loads. The eddy current loss of each loop in the copper plate is calculated, at the rated slip speed. Then, the thermal resistance network is carried out, in which the previously obtained eddy current losses are heat sources for calculating the copper plate node temperature. In the thermal study, the influence of various loads on copper plate node temperature rise is analyzed. Finally, the analytical predicted results are compared with the results of finite element method and measurement. The comparison results confirm the validity of the electromagnetic–thermal model.

Analysis of Torque Characteristics according to Non-uniform Air Gaps of Coaxial Magnetic Gear

Eui-Jong Park,Chan-Seung Kim,Sang-Yong Jung,Yong-Jae Kim Korean Magnetics Society 2018 Journal of Magnetics Vol.23 No.4

Recently, studies on magnetic gears have been actively conducted. Magnetic gears can replace mechanical gears as they can perform noncontact power transfer, thereby minimizing loss and damage from friction. A magnetic gear has two rotors with different numbers of poles because of its structural characteristics. For a rotor with a relatively lower number of poles, large torque ripples occur owing to the increase in the permeance variation within the air gaps. Other electric equipment studies conducted thus far have primarily changed the shape of iron core to reduce torque ripples. However, since the magnetic gear has two air gaps, it is necessary to identify the relationship between the two gaps and the ripple before changing the shape of the iron core. In this paper, factors that affect torque ripple are classified and analyzed by examining the magnetic flux density of two air gaps, to propose an air gap structure that benefits the design of magnetic gears.

Detailed Magnetic Force Analysis of A 4-Pole Hybrid Electromagnet by Magnetic Equivalent Circuit Method

Hasan Fatih Ertu?rul,Kadir Erkan,Huseyin Uvet Korean Magnetics Society 2018 Journal of Magnetics Vol.23 No.4

In this paper, detailed magnetic force analysis of a 4-pole hybrid electromagnet system providing an advantage of full-redundant levitation is studied. The novel fragmented magnetic equivalent circuit method (MEC) is developed to accurately capture inherited nonlinear characteristics of 4-pole hybrid electromagnet to investigate force characteristics and magnetic field distribution. To confirm this method, two possible scenarios, which are levitation under plain core and levitation under dual-linear motor are composed. As well as, they are examined by both proposed method and FEM analyses. Comparative analyses of both methods revealed that force, inclination torque, and mutual interference can be easily captured with adequate accuracy while at the same time yielding less computation and set up time. Furthermore, the fragmented formulations of permeance functions can be generalized for the analysis and the design of similar devices which specifically involve inclination motions.

A Novel Semi-inserted Dual-stator Low-speed High-torque Permanent Magnet Drive Motor

Jiwei Liu,Xiaohua Bao,Youyuan Ni,Mingji Zou Korean Magnetics Society 2018 Journal of Magnetics Vol.23 No.4

Low-speed high-torque permanent magnet direct drive machine (LSPMDM) overcomes the shortcomings of traditional drive system, but its volume is large. In this paper, the numerical relationship between the motor external diameter and the rated speed is deduced, and improvement of the torque density is qualitatively analyzed for a dual-stator motor. Owing to that semi-inserted magnetic circuit structure and auxiliary slots under the poles can further increase the torque density of the motor, the effect of the shape, number and position of the auxiliary slots on the salient pole rate is also studied through comparative analysis. By incorporating the merits of dual-stator motor and semi-inserted magnetic circuit structure with the auxiliary slots, a novel motor topology is proposed, which is verified by finite element analysis with good performance.

Analysis of Direction and area of Magnetic Susceptibility Artifact according to Frequency-encoding Changes in 3.0 Tesla MRI

Ji-Won Kim,Wan-Sik Park,Hyun-Sung Kim,Soo-Chul Kim,Yoon-Heui Kang,Tae-Kun Kim,Dong-Kyoon Han,Yeong-Cheol Heo Korean Magnetics Society 2018 Journal of Magnetics Vol.23 No.4

In this study, the length and area of t he artifact were quantitatively evaluated according to the direction of the magnetic susceptibility artifact. Using a self-made magnetic susceptibility artifact phantom the frequencyencoding direction in the 3.0T MRI system was changed in axial, coronal, and sagittal planes using T2 fast spin echo (FSE). The results showed a difference in length when the frequency encoding was changed from anteroposterior (AP) to right-to-left (RL) in the axial, RL to superior-inferior (SI) in coronal and AP to SI in sagittal planes (p < 0.05). In addition, the difference occurred when the magnetic susceptibility artifact area was measured according to the frequency-encoding direction conversion (p < 0.05). However, additional studies of magnetic susceptibility artifacts using various types of screws and plates are needed. This study provides basic data to prevent magnetic susceptibility artifact due to screw fixation.

3D Helmholtz Coil-based Hybrid Manipulation for Active Locomotion of Magnetic Micro/Nano Robots

Sung Hoon Kim Korean Magnetics Society 2018 Journal of Magnetics Vol.23 No.4

This study presents hybrid control based on three-axis Helmholtz coil for manipulation of magnetic micro/nano robots. In general, magnetic force and torque control requires both Maxwell and Helmholtz coils. Therefore, the configuration of the magnetic manipulation system is complex and requires many power supplies. The hybrid method controls the three-axis Helmholtz coil and three power supplies through mechanical switch control to generate magnetic force and torque. Magnetic torque is controlled by the three-axis Helmholtz coil with a rotating magnetic field, and magnetic force is controlled by generating gradient magnetic field through the separated coils by the switch control. Three switches separate each Helmholtz coil and six switches control the separated six coil with the three power supplies. The hybrid control can provide simple configuration of coil system, various active locomotion, and precision control in complex environments. To verify the proposed method, we conducted magnetic simulation with various experimental tests.

Synthesis and Magnetic Properties of Electrodeposited Cobalt-Iron-Vanadium Thin Films

Chae, Kwang-Pyo The Korean Magnetics Society 2006 Journal of Magnetics Vol.11 No.2

CoFeV thin film alloys were fabricated by electrodeposition, and the dependences of their magnetic properties on the current density were investigated using an X-ray diffractometer and a vibrating sample magnetometer. The deposited Co increased from about 45 to 60 wt.% with increasing current density until $25mA/cm^2$ whereas the deposited Fe decreased from about 55 to 40 wt.% with increasing current density until $25mA/cm^2$. The deposited V, about 2 wt.%, was independent of the current density. The current efficiencies of electrodeposition decreased linearly from about 40 to 29% with increasing current density. The X-ray diffraction measurement showed that all peaks of the CoFeV films were consistent with those of a typical Co hcp and Fe bcc mixed phase. An increase in the current density decreased the grain size and increased the lattice constant. The saturation magnetization increased from about 2.2 to 2.5 T with increasing current density. The coercivity measured in the perpendicular direction decreased from 260 to 120 Oe with increasing current density; a drastic drop of 60 Oe occurred at $5mA/cm^2$. The coercivity measured in the in-plane direction remained almost unchanged, at about 20 Oe, with increasing current density.