• Journal of Powder Materials
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• v.10 no.5
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• pp.333-336
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• 2003

The purpose of this study is the fabrication of nano-sized Fe-Co alloy powders with soft magnetic properties by the slurry mixing and hydrogen reduction (SMHR) process. $FeCl_2$0 and $CoCl_2$ powders with 99.9% purities were used for synthesizing nanostructured Fe-Co alloy powder. Nano-sized Fe-Co alloy powders were successfully fabricated using SMHR, which was performed at 50$0^{\circ}C$ for 1 h in H$_2$ atmosphere. The fabricated Fe-Co alloy powders showed $\alpha$' phase (ordered body centered cubic) with the average particle size of 45 nm. The SMHR powder exhibited low coercivity force of 32.5 Oe and saturation magnetization of 214 emu/g.

• Journal of Magnetics
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• v.11 no.4
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• pp.167-169
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• 2006

Nanocrystalline CoFeHfO thin films have been fabricated by RF sputtering method. It is shown that the CoFeHfO thin films possess not only high electrical resistivity but also large saturation magnetization and anisotropy field. Among the composition investigated, $Co_{53}FE_{22}Hf_{10}O_{15}$ thin film is observed to exhibit good soft magnetic properties: coercivity ($H_{c}$) of 0.18 Oe; anisotropy fild ($H_{k}$) of 49.92 Oe; saturation magnetization ($4{\Pi}M_{s}$) of 15.5 kG. The frequency response of permeability of the film is excellent. The excellent magnetic properties of this film in addition of an extremely high electrical resistivity (r) of $185\;{\mu}cm$ make it ideal for uses in high-frequency applications of micromagnetic devices. It is the formation of a peculiar microstructure that resulted in the superior properties of this film.

• Journal of the Korean institute of surface engineering
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• v.29 no.6
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• pp.847-850
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• 1996

The bi-layered films composed of Co-Cr-Ta layers and paramagnetic $Co_{67}Cr_{33}$ underlayer were deposited by suing Facing Targets Sputtering(FTS). The effects of $Co_{67}Cr_{33}$ underlayer on the crystallographic and magnetic characteristics of the Co-Cr-Ta layer deposited on the underlayer was investigated. The diffraction intensity $I_{p(002)}$ of Co-Cr-Ta layers on the $Co_{67}Cr_{33}$ layer was stronger than that of single layer and Co-Cr-Ta/Ti double layer. Therefore, the crystallinity of Co-Cr-Ta layer was imporved by the $Co_{67}Cr_{33}$ underlayer rather than Ti ones. However, te coercivity H$_{c\bot}$ of Co-Cr-Ta layers deposited on $Co_{67}Cr_{33}$ underlayer was as low as 250 Oe even at substrate temperature of $220^{\circ}C$. This H$_{c\bot}$ decrease seems to be attributed to the effect of the $Co_{67}Cr_{33}$ underlayer as well as interval time between deposition of the underlayer and the Co-Cr-Ta layer.

• Journal of Magnetics
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• v.7 no.3
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• pp.72-79
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• 2002

Local M-H loops have been measured on the free layer of a tunneling magnetoresistance (TMR) junction using the magneto-optical Kerr effect (MOKE) system, with an optical beam size of about 2 $\mu$m diameter. Tunnel junctions were deposited using the DC magnetron sputtering method in a chamber with a base pressure of 3$\times$10$^{-9}$ Torr. The relatively irregular variations of coercive force H$_c$(∼17.5 Oe) and unidirectional anisotropy field H$_{ua}$(∼7.5 Oe) in the as-deposited sample are revealed. After $200{^{\circ}C}$ annealing, He decreases to 15 Oe but H$_{ua}$ increases to 20 Oe with smooth local variations. Two-dimensional plots of H$_c$ and H$_{ua}$ show the symmetric saddle shapes with their axes aligned with the pinned layer, irrespective of the annealing field angle. This is thought to be caused by geometric effects during deposition, together with a minor annealing effect. In addition, the variation of root mean square (RMS) surface roughness reveals it to be symmetric with respect to the center of the pinned-layer axis, with the roughness of 2.5 $\AA$ near the edge and 5.8 $\AA$ at the junction center. Comparison of surface roughness with the variation of H$_{ua}$ suggests that the H$_{ua}$ variation of the free layer is well described by dipole interactions related to surface roughness. As a whole, the reversal magnetization is not uniform over the entire junction area and the macroscopic properties are governed by the average sum of local distributions.

• Proceedings of the KIPE Conference
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• 2003.07b
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• pp.824-827
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• 2003

Recently, Development of Rare Earth Permanent magnet with the high remanence, high coercivity allow the design of brushless motors with very high efficiency over a wide speed range. Cogging torque is produced in a permanent magnet by magnetic attraction between the rotor mounted permanent magnet and the stator teeth. It is an undesired effect that contributes to the machines output ripple, vibration, and noise. This cogging torque can be reduced by variation of magnet arc length, airgap length, magnet thickness, shifting the magnetic pole and varying the radial shoe depth and etc. In this paper, Some airgap length and magnet arc that reduce cogging torque are found by FEM(Finite element method). The SPM type of high-capacity BLDC motor is optimized as a sample model.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.4
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• pp.453-459
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• 2004

In this experiment, flux method was applied for preparing ferroxplana at low temperature, The common salt was used as a flux. The mole ratio of flux to Zn$_2$Y was varied with 0, 6.5, 13, 26 and 52 in dry ball-mixing. Zn$_2$Y was obtained after heat treatment of the mixed powder. Crystallization, particle morphology and magnetic properties of the prepared powder were investigated using XRD, VSM and SEM. The ferroxplana powder of 2-4 ${\mu}{\textrm}{m}$ was obtained with the mole ratio 26 by heat treating at the temperature of 110$0^{\circ}C$. The coercivity(H$_{c}$) and saturation magnetization(M$_{s}$) of the ferroxplana were 282Oe and 64.5emu/g, respectively.y.y.

• Journal of Magnetics
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• v.22 no.1
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• pp.7-13
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• 2017

The magnetoresistance (MR) properties of antiferromagnetic (AFM) IrMn based giant magnetoresistance-spin valve (GMR-SV) was investigated in view point of the artificial rotation effect of ferromagnetic (FM) layer in the plane induced by an applied field during the post annealing temperature. The MR curves measured with an azimuthal angle region of ${\phi}=0^{\circ}-360^{\circ}$ are depended on the annealing temperature and the magnetization easy axis of two free NiFe layers and two pinned NiFe layers in dual-type GMR-SV film. Especially, the annealing temperature and sample rotation angle(${\theta}$ ) maintained to the magnetic sensitivity (MS) of 1.4 %/Oe with an isotropic region angle of $110^{\circ}$ are $100^{\circ}C$ and $90^{\circ}$, respectively.

• Applied Microscopy
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• v.47 no.1
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• pp.29-35
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• 2017

Transverse magnetic field annealing (TFA) was carried out on $Fe_{73.5}Cu_1Nb_3Si_{15.5}B_7$ nano-crystalline magnetic core with the aim at decreasing coercivity ($H_c$) while keeping high inductance ($L_s$). The magnetic field generated by direct current (DC) was applied on the magnetic core during different selected annealing stages and it was proved that the nanocrystalline magnetic core achieved lowest $H_c$ when applying transverse field during the whole annealing process (TFA1). Although the microstructure and crystallization degree of the nanocrystalline magnetic core exhibited no obvious difference after TFA1 compared to no field annealing, the TFA1 sample showed a more uniform nanostructure with a smaller mean square deviation of grain size distribution. $H_c$ of the nanocrystalline magnetic core annealed under TFA1 decreased along with the increasing magnetic field. As a result, the certain size nanocrystalline magnetic core with low $H_c$ of 0.6 A/m, low core loss (W at 20 kHz) of 1.6 W/kg under flux density of 0.2 T and high $L_s$ of $13.8{\mu}H$ were obtained after TFA1 with the DC intensity of 140 A. The combination of high $L_s$ with excellent magnetic properties promised this nanocrystalline alloy an outstanding economical application in high frequency transformers.

• Resources Recycling
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• v.12 no.6
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• pp.13-18
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• 2003

The initial NiCuZn synthetic ferrite were acquired from thermally decomposing the metal nitrates Fe($NO_3$)$_3$ㆍ$9H_2$O, Zn($NO_3$)$_2$ㆍ$6H_2$O, Ni($NO_3$3)$_2$ㆍ $6H_2$O and Cu(NO$_3$)$_2$ㆍ $3H_2$O at 1$50^{\circ}C$ for 24 hours and was calcined at $500^{\circ}C$. Each of those was pulverized for 3 and 9 hours in a steel ball mill and was sintered between $700^{\circ}C$ and $1,000^{\circ}C$ for 1 hour, and then their microstructures and magnetic properties were examined. We could make the initial specimens chemically bonded in liquid at the temperature as low as $150 ^{\circ}C$, by using the melting points less than $ 200^{\circ}C$ of the metal nitrates instead of the mechanical ball milling, then narrowed a distance between the particles into a molecular level, and thus lowed sintering temperature by at least $200 ^{\circ}C$ to $300^{\circ}C$ Their initial permeability was 50 to 490 and their saturation magnetic induction density and coercive force 2,400G and 0.3 Oe to 1.2 Oe each, which were similar to those of NiCuZn ferrite synthesized in the conventional process.

• Journal of the Korean Magnetics Society
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• v.11 no.4
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• pp.146-150
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• 2001

The effect of H$_2$ content in Ar sputtering gas on exchange coupling field(H$_{ex}$) for NiFe/FeMn interface was studied. When NiFe layer of Si(100)/Ta(50 $\AA$)/NiFe(60 $\AA$)/FeMn(250 $\AA$)Ta(50 $\AA$) was deposited at 8% H$_2$ in sputtering gas, the maximum exchange coupling field(H$_{ex}$) and minimum coercivity(H$_{c}$) were obtained. When Si(100)/Ta(50 $\AA$)/NiFe(60 $\AA$)/FeMn(250 $\AA$)/NiFe(70 $\AA$)/Ta(50 $\AA$) was deposited at 5% H$_2$ in sputtering gas, the maximum exchange coupling field(H$_{ex}$) of 148 Oe was obtained. The (111) preferred orientation and grain size of underlayer NiFe were increased and the internal stress was reduced by H$_2$ in sputtering gas. And the (111) preferred orientation and grain size of FeMn layer were also increased.d.ased.