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Properties of Iron Powder Compressed Cores with Magnetite Thin Film Insulator
Pyungwoo Jang(장평우) 한국자기학회 2020 韓國磁氣學會誌 Vol.30 No.1
It is very important to isolate soft magnetic particles electrically in order to reduce an eddy current loss of compressed cores. In this study, iron powders were oxidized in a mixed gas of N<SUB>2+</SUB>H₂O at 600℃ in order to encapsulate the powders completely by iron oxide and compressed into cores. The oxide film was analyzed to be Fe₃O₄ by XRD as well as its color and grew linearly through oxidation. With increasing oxidation time, its permeability increased whereas the density decreased. The core, eddy current and hysteresis losses of the oxidized cores were much lower than those of the cores with insulating powders. It was confirmed that the Fe₃O₄ film formed in a damp atmosphere could encapsulate the iron particles completely and ensured lower eddy current loss.
Properties of Fe-Al Cores Made From Fe-Al Powders Annealed in a Damp Hydrogen Atmosphere
Pyungwoo Jang,Seungchan Shin IEEE 2013 IEEE transactions on magnetics Vol.49 No.1
<P>Gas-atomized Fe-4, 6wt.%Al powders were annealed in a damp hydrogen atmosphere with a dew point of 0<SUP>°</SUP>C and -17<SUP>°</SUP>C in order to cover the powder surface with a high electrical resistivity layer of Al<SUB>2</SUB>O<SUB>3</SUB> and then compressed into cores. The powders should be oxidized at a temperature higher than 800 <SUP>°</SUP>C in order to oxidize the aluminum alone on the surface of powder, as confirmed by simulation using the STANJAN program. An Al-rich layer, i.e., an Al<SUB>2</SUB>O<SUB>3</SUB> layer, was formed on the surface of the Fe-Al powder, as confirmed by SEM. Loss of the cores made from the selectively oxidized powders was much lower than those of the cores with phosphate coats, so the selectively oxidized powder can be used to fabricate electrical actuators with high levels of performance.</P>
정현파 자속밀도 제어와 디지털 궤환을 이용한 AC 손실 측정방법
장평우(Pyungwoo Jang) 한국자기학회 2012 韓國磁氣學會誌 Vol.22 No.1
New digital feedback algorithm was developed to measure iron loss of soft magnetic materials under a condition of sinusoidal flux waveform. V<SUB>in</SUB>(B) curve was used instead of H(B) curve to decide next input waveform in the feedback module so that adjusting phases of current waveform, flux waveform, and input waveform could be removed. The effectiveness of the developed algorithm was verified when iron loss of ferrite cores was measured under frequencies of 1 and 10 kHz.
장평우(Pyungwoo Jang) 한국자기학회 2016 韓國磁氣學會誌 Vol.26 No.1
Effects of annealing of the gas-atomized Fe-9%Si-2%Cr powder which is suitable for high frequency application in mobile devices because of its high electrical resistivity were studied with an emphasis on the order-disorder phase transition. The formation of B2 ordered phase could not be suppressed during atomization process. When the powder was annealed at a temperature higher than 550 ℃ the peak diffracted from DO<SUB>3</SUB> phase could be detected. With increasing annealing temperature lattice parameter and coercivity decreased. An interesting phenomenon was an abrupt increment of coercivity in the powder annealed at 450 ℃. Highest permeability could be shown in the powder annealed at a relative low temperature of 150 ℃ and then the permeability decreased with annealing temperature. The above-mentioned results could be successfully explained by both the formation of DO<SUB>3</SUB> ordered phases and the change of electrical resistivity of the Fe-Si-Cr powder which was also originated from the phase transition.
장평우(Pyungwoo Jang),이봉한(Bonghan Lee),최광보(Gwangbo Choi) 한국자기학회 2010 韓國磁氣學會誌 Vol.20 No.1
Fe-3, 4.2 and 6.8% Si compressed cores were fabricated, and then electrical resistivity, AC and DC magnetic properties, microhardness, and other properties were analyzed in order to know whether best soft magnetic properties could be also obtained in an Fe-Si compressed core with the well-known composition of Fe-6.5% Si. With increasing the silicon content, eddy current loss and hysteresis loss decreased and increased, respectively, so that a minimum total loss was not obtained in the well-known Fe-6.8 % Si cores, but obtained in the Fe-4.2 % Si cores. Also electrical resistivity of the cores and hardness of the particles increased monotonously with silicon content so that compaction ratio of the cores decreased. B2 and DO₃ ordered phase could be observed only in Fe-6.8% Si powder. A minimum loss and highest permeability of the Fe-4.2 % Si cores can be explained by the ratio of specific electrical resistivity of insulator to that of magnetic particles, micro-hardness, compaction ratio and demagnetization coefficient of the Fe-Si powder particles with silicon content.
장평우(Pyungwoo Jang),김종렬(Jongryul Kim) 한국자기학회 2005 韓國磁氣學會誌 Vol.15 No.1
Magnetic properties of YIG films grown by solid phase epitaxy (SPE) was measured as a function of temperature with focus on magneto-crystalline and perpendicular magnetic anisotropy. Perpendicular magnetic anisotropy was not induced in the SPE YIG films annealed at low temperature by relaxing residual stress through formation of dislocation. On the contrary the films annealed at high temperature showed perpendicular magnetic anisotropy which shows very low density of dislocation. Perpendicular magnetic anisotropy field decreased linearly up to a high temperature of 230℃ above which magneto-crystalline anisotropy disappeared. Coercivity also decreased linearly with temperature up to 230℃. Magneto-crystalline anisotropy of perpendicular anisotropy induced epitaxial (111) YIG films can be measured using Hk= 4K₁/3Ms . Temperature behavior of initial susceptibility can be successfully explained by Hopkinson effects. Curie temperature of YIG films grown on GGG substrate with high paramagnetic susceptibility can be easily measured using the results.
열처리온도가 고상에피택시 YIG박막의 특성에 미치는 영향
장평우(Pyungwoo Jang) 한국자기학회 2003 韓國磁氣學會誌 Vol.13 No.6
Effects of annealing temperature on the crystalline and magnetic properties of YIG films grown by solid phase epitaxy. The eptiaxy films were made by annealing Fe-Y-O amorphous films in the air at 550-1050 ℃ which were sputtered on GGG (111) substrates in a conventional rf sputtering system. Crystallization temperature of Fe-Y-O amorphous films on GGG (111) substrate was between 600 and 650 ℃ which is much lower than that Fe-Y-O powder prepared by sol-gel method. Excellent epitaxial growth of YIG films could be conformed by the facts that the diffraction intensity of YIG (888) plane was comparable with that of GGG (888) plane and full width at half maximum of YIG (888) rocking curve was smaller than 0.14° when films were annealed at 1050 ℃. It could be seen that it is necessary to anneal the films at higher temperature for an excellent epitaxy because lattice parameter of YIG films were smaller and the peak of YIG (888) plane is higher and narrower with increasing annealing temperature. Films annealed at higher temperature shows M-H loop with perpendicular anisotropy which was due to 0.15% lattice mismatch between YIG and GGG.