• Title/Summary/Keyword: Remanence

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Variation of Magnetic Properties of (Nd, Dy)-Fe-B Sintered Magnets with Compaction Conditions ((Nd, Dy)-Fe-B 소결자석의 성형조건에 따른 자기특성 변화)

  • NamKung, S.;Lee, M.W.;Han, S.J.;Jang, T.S.
    • Journal of Powder Materials
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    • v.19 no.1
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    • pp.1-5
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    • 2012
  • In order to improve the remanence of (Nd, Dy)-Fe-B sintered magnets, we investigated the influence of compaction conditions such as packing density, applied field and green density on the magnetic properties. While the remanence decreased with increasing the packing density and green density, it increased with the increase of the applied field. In addition, XRD analysis revealed that the remanence was enhanced as the degree of powder alignment was improved. The green density was more influential on the remanence than the packing density and applied field.

Magnetic Properties of Magnetites at Low Temperatures (자철석의 저온 자화특성)

  • Hong, Hoa-Bin;Yu, Yong-Jae
    • Journal of the Mineralogical Society of Korea
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    • v.24 no.1
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    • pp.37-42
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    • 2011
  • Magnetic properties at low-temperatures can diagnose the presence of certain magnetic minerals in rocks. At the Verwey transition temperature ($T_v$, ~105~120 K), magnetite transforms from monoclinic to cubic structure as the temperature increases. At the isotropic point ($T_i$, ~135 K), magnetocrystalline anisotropic constant of magnetite passes through zero (from negative to positive) as the temperature decreases so that its optimal remanence acquisition axis changes from [111] to [001]. A sharp remanence drop was observed at $T_v$ during warming of LTSIRM (low-temperature saturation isothermal remanent magnetization). For cooling of RTSIRM (room-temperature saturation isothermal remanent magnetization), the remanence decreased on passing $T_i$ and $T_v$. On warming of RTSIRM, remanence recovery becomes more prominent as the average grain size of magnetite increases. In summary, the SIRM memory decreases with increasing grain size of magnetite. A similar, but rather gradual, remanence transition occurs for natural samples due to contribution of cations other than Fe. As a non-destructive tool, low-temperature magnetic behavior is sensitive to unravel the magnetic remanence carriers in terrestrial rocks or meteorites.

Evaluation of Aging Degradation in 2.25Cr-1Mo Steel by Coercivity and Remanence Measurements - Microstructural Approach (보자력 및 잔류자화를 이용한 2.25Cr-1Mo강의 경년열화도 평가 - 미세조직적 접근)

  • Byeon, Jai-Won;Kwun, Sook-In
    • Journal of the Korean Society for Nondestructive Testing
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    • v.22 no.1
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    • pp.65-73
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    • 2002
  • Artificial aging was performed to simulate the microstructural degradation in 2.25Cr-1Mo steel arising from long time exposure at $540^{\circ}C$. Microstructural analysis (mean equivalent size, number of carbides per unit area) and measurement of mechanical properties(UTS, Vickers hardness) and magnetic properties(coercivity, remanence) were performed. By comparing these results, the relationship between magnetic properties and microstructural changes with artificial aging was clarified. The carbides were classified as rod, globular and acicular type in terms of morphology. The fine acicular carbides were found to diminish drastically in the initial stage of aging. The magnetic coercivity and remanence were observed to decrease rapidly in the initial about 920 hours of aging time and then decrease slowly afterwards. Linear correlations between the mechanical properties and magnetic properties such as correlations remanence were found.

Evaluation of Microstructures and Mechanical Property of Variously Heat Treated 0.85% Carbon Steel by Magnetic Method (자기적 방법에 의한 0.85% 탄소강의 열처리에 따른 미세조직 및 기계적 성질 평가)

  • Byeon, Jai-Won;Kwun, S.I.
    • Korean Journal of Materials Research
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    • v.13 no.2
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    • pp.81-87
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    • 2003
  • Microstructures and mechanical properties of variously heat treated 0.85% carbon steel(eutectoid steel) were evaluated by magnetic property measurements. Microstructural analysis (pearlite interstellar spacing), measurement of mechanical properties(Rockwell hardness, yield stress, fracture stress) and magnetic properties(coercivity, remanence, hysteresis loss, saturation magnetization) were performed to clarify mutual relationships among these parameters. Water quenched specimens with martensite structure showed much higher coercivity and remanence than air cooled or furnace cooled specimens with pearlite structure. The linear dependence of coercivity and remanence on pearlite interlamellar spacing as well as on Rockwell hardness, yield stress and fracture stress was observed in the pearlitic steel. Hysteresis loss and saturation magnetization showed no distinct trend with pearlite interlamellar spacing.

Changes of Carbide Characteristics and Magnetic Properties in Artificially Aging Heat Treated 2.25CrMo Steel (경년열화 열처리된 2.25CrMo 강에서의 탄화물 특성 및 자기적 성질의 변화)

  • Byeon, Jal Won;Kwun, S.I.
    • Journal of the Korean Society for Heat Treatment
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    • v.14 no.6
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    • pp.323-329
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    • 2001
  • Artificial aging was performed to simulate the microstructural degradation in 2.25CrMo steel arising from long time exposure at $540^{\circ}C$. The carbide morphologies were classified as acicular, pipe and globular type, and the number of carbides per unit area was measured for each type of carbides. The fine acicular carbides were found to diminish drastically in the initial stage of aging. An attempt was made to evaluate the microstructural degradation in artificially aging heat treated 2.25CrMo steel by the magnetic property measurements such as saturation magnetization, coercivity and remanence. The saturation magnetization showed no distinct trend with aging time. However, the coercivity and remanence were observed to decrease rapidly in initial 920 hours of aging time and then decrease slowly afterwards.

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The Effect of CuO and SiO2 on the Magnetic Properties of Sr-Ferrite (CuO와 SiO2가 Sr-페라이트의 자기적 특성에 미치는 영향)

  • 김동식;김동엽;정원용;오재현
    • Journal of the Korean Ceramic Society
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    • v.26 no.6
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    • pp.747-754
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    • 1989
  • The effects of CuO and SiO2 on the sintered density, grain growth and magnetic properties of Sr-ferrite were investigated. The sintered density of Sr-ferrite is increased with increasing the amount of CuO or SiO2 addition. The grain of Sr-ferrite grow uniformly with the addition of CuO, so remanence increases and coercivity decreases. The addition of SiO2 increase coercivity but does not affect remanence prominently. The sintering temperature above 125$0^{\circ}C$ and SiO2 addition above 0.8wt% causes abnormal grain growth in Sr-ferrite. When CuO and SiO2 are added simultaneouly, remanence does not decrease but coercivity shows low value.

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COMPUTER SIMULATION OF MAGNETIC PROPERRTIES OF SPRING MAGNETS

  • Kitajima, N.;Inoue, H.;Kanai, Y.;Fukunaga, H.
    • Journal of the Korean Magnetics Society
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    • v.5 no.5
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    • pp.404-407
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    • 1995
  • Magnetic properties of model exchange-spring magnets, which are composed of magnetically soft and hard grains, were calculated by means of computer simulation. The dependence of the magnetic properties on the strength of intergrain exchange interaction and the amount of soft grains was studied. The existence of soft grains enhanced the remanence remarkably, and the remanence over $0.8M_{s}$ was obtained in the model magnets containing 25% or more soft grains by volume. The calculated coercivity vs. the strength of the exchange interaction curves showed a peak at a critical strength of the exchange interaction, although the remanence increased monotonously with increase in the strength of the exchange interaction. Thus the maximum energy product also reached a peak around the same critical strength. The calculated maximum energy product exceeded $300kJ/m^{3}$ when the magnet is assumed to be composed of $Fe_{3}B$ and $Nd_{2}Fe_{14}B$.

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Magnetism of Ferric Iron Oxide and Its Significance in Martian Lithosphere (화성 암권의 진화해석을 위한 예비연구: 3가철 산화물의 자화특성)

  • Jeong, Doo-Hee;Yu, Yong-Jae
    • Journal of the Mineralogical Society of Korea
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    • v.24 no.3
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    • pp.189-194
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    • 2011
  • Martian satellite missions indicate that Martian equatorial plains are covered by ferric iron oxide. As a non-destructive technique, low-temperature treatment of remanent magnetization is effective in identifying magnetic minerals in rocks. In the present study, four sets of ferric iron oxides were prepared by aqueous alteration of ferrihydrite at warm conditions and four others by dehydration of goethite. As the amount of aluminous trivalent cations increases, crystallographic lattice parameters and N$\acute{e}$el temperatures decrease. Such declines originate from lattice distortion as the smaller aluminous trivalent cations substitue the larger terric irons. Whilst high remanence memory was observed for aqueously produced ferric iron oxide, low remanence memory was observed for dehydrated ferric iron oxide. In the future. magnetic remanence memory would be powerful in diagnosing the origin of ferric iron oxide.

Relationship Between AC and DC Magnetic Properties of an Iron-Based Amorphous Alloy for High Frequency Applications

  • Choi, Y.S.;Noh, T.H.;Lim, S.H.
    • Journal of Magnetics
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    • v.1 no.1
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    • pp.24-30
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    • 1996
  • The relationship between effective permeability and the remanence ratio of an Fe-based amorphous alloy (Metglas 2605S3A) is investigated over a wide frequency range, in an effort to understand magnetization behavior of the alloy. In the frequency range from 1 to 200 kHz, the permeability is maximum at the remanence ratio of 0.4-0.5 and, at frequencies over 500 kHz, the correlation with negative coefficients emerges indicating that the permeability decreases with the remanent ratio, except for the ribbon coated with an insulating layer of MgO which exhibits both high values of the effective permeability and remanence ratio. It is considered from the correlation results that the boundary at which the dominant magnetization mechanism changes from domain wall motion to spin rotation is near 500 kHz. The core loss is also investigated as a function of annealing time when the samples are annealed at a fixed temperature of $435^{\circ}C$. The core loss in most cases decreases with the annealing time, the degree of the loss may consist of the hysteresis loss and anomalous eddy current loss. The two loss components are considered to be of similar magnitudes at low frequencies while, at high frequencies, the dominant contribution to the total loss is the anomalous loss.

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Improvement of Microstructural Anisotropy of Nd-Fe-B-Ga-Nb Alloy by the Control of Hydrogen Reaction (수소반응속도 제어에 의한 Nd-Fe-B-Ga-Nb 합금의 미세조직 이방화율 향상에 관한 연구)

  • Lee, S.H.;Kim, D.H.;Yu, J.H.;Lee, D.W.;Kim, B.K.
    • Journal of Powder Materials
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    • v.17 no.1
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    • pp.23-28
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    • 2010
  • HDDR treated anisotropic Nd-Fe-B powders have been widely used for the sheet motors and the sunroof motors of hybrid or electric vehicles, due to their excellent magnetic properties. Microstructural alignment of HDDR treated powders are mostly depending on the hydrogen reaction in disproportionation step, so the specific method to control hydrogenation reaction is required for improving magnetic properties. In disproportionation step, hydrogenation pressure and reaction time were controlled in the range of 0.15~1.0 atm for 15~180 min in order to control the micorstructural alignment of $Nd_2Fe_{14}B$ phase and, at the same time, to improve remanence of HDDR treated magnet powders. In this study, we could obtain a well aligned anisotropic Nd-Fe-B-Ga-Nb alloy powder having high remanence of 12 kG by reducing hydrogen pressure down to 0.3 atm in disproportionation step.