• 한국표면공학회지
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• 제29권6호
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• pp.644-647
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• 1996

The distribution of coercivity in the thickness direction were investigated by using Kerr hysteresis loop tracer for the Co-Cr films deposited by Facing Targets Sputtering apparatus. It was found that the difference between the coercivities of surface layer and initial growth layer H$_c$$\bot$(S)-H$_c$$\bot$(I) correlated strongly with $\Delta$H$_o$, shich represents the degree of distribution of coercivity. Furthermore, the Cr content was varied in order to improve the coercivity of imitial growth layer H$_c$$\bot$(I) and distribution of coercivity. H$_c$$\bot$(I) took a maximum value of 750 Oe and the distribution of coercivity became sharper at the Cr content of 25at. %.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 C
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• pp.1320-1322
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• 1997

The distribution of coercivity in the thickness direction were investigated by using Kerr hysteresis loop tracer for the Co-Cr films deposited by Facing Targets Sputtering apparatus. It $H_{c{\bot}}(S)- H_{c{\bot}}(I)$ correlated strongly with ${\Delta}H_c$, which represents the degree of distribution of coercivity. Furthermore, the Cr content was varied in order to improve the coercivity of intial growth layer $H_{c{\bot}}(I)$ took a maximum value of 750 Oe and the distribution of coercivity became sharper at the Cr content of 25 at.%.

• 한국자기학회지
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• 제5권5호
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• pp.663-666
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• 1995

The domain wall motion coercivity, $H_{c}$, of magnetic materials arises from the dependence of the wall energy on localized changes in material parameters (magnetization, anisotropy, exchange energy densities). However, in an otherwise perfectly homogeneous material, the domain wall energy might change due to the change in the volume of the wall versus the wall position. Thus, any surface roughness contributes to the coercivity. Assuming different two-dimensional surface profiles, characterized by average wavelengths ${\lambda}_{x}$ and ${\lambda}_{y}$, and relative thickness variations dh/h, the coercivity due to the surface roughness has been calculated. Compared to the one dimensional case, the 2D coercivity is reduced. Depending on the ratio of ${\lambda}$ to the domain wall width, $H_{c}$ has a maximum around 2, and increasing with dh/h. With the decreasing thickness of the thin film and GMR heads, it might be the domain factor in determining the coercivity.

• 한국자기학회지
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• 제5권3호
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• pp.216-221
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• 1995

자성분말의 보자력$(H_{c})$과 보자력 분포도는 조성 이외의 제조공정인자에 크게 의존하는 값으로 자성분말 제조시 재현성을 결정하는 중요한 물성중의 하나이다. 자성분 말의 자기적 물성을 측정하는 VSM을 이용하여 쉽고 간단하게 보자력 분포도를 측정하는 방법과 그 응용예를 제시하였다. 보자력 분포도 측정은 magnetic hysteresis loop 의 dM/dH 대 H 곡선의 형태와 반치폭에서 얻을 수 있다. dM/dH 곡선 형태가 분리되는 것 없이 반치폭이 작아질수록 보자력 분포도는 더 균일해짐을 나타낸다. 보자력이 다 른 Ba-Ferrite와 ${\gamma}-Fe_{2}O_{3}$ 혼합물 중 Ba-Ferrite의 $H_{c}$가 높아질수록 dM/dH 대 H 곡선 형태는 peak broadening 후 peak splitting으로 나타나며, 이 peak splitting은 혼합자성분말의 $H_{c}$ 차이가 600 Oe 이상일 때 일어난다. 또한 dM/dH 대 H 곡선의 응용으로는 자성분말 보자력 분포도 측정, Ba-Ferrite 구조내로 dopants의 치환 능력 및 ${\alpha}-Fe$의 산화거동을 연구하는데 사용될 수 있다.

• Journal of Magnetics
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• 제17권3호
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• pp.185-189
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• 2012

The coercivity of near single domain size $Nd_2Fe_{14}B$-type particles prepared by ball milling of HDDR-treated $Nd_{12.5}Fe_{80.6}B_{6.4}Ga_{0.3}Nb_{0.2}$ alloy was investigated. The feasibility of a surface nitrogenation for improving the coercivity stability of the fine $Nd_2Fe_{14}B$-type particles was also studied. The near single domain size $Nd_2Fe_{14}B$-type particles had a high coercivity of over 9 kOe. However, the coercivity radically deteriorated as the temperature increased in air (< 2 kOe at $200^{\circ}C$). This coercivity reduction was attributed to the soft magnetic phases, ${\alpha}$-Fe and $Fe_3B$, which formed on the surface of the fine particle due to oxidation. Surface nitrogenation of the fine particles significantly improved the stability of their coercivity. The improvement in coercivity stability was attributed to the formation of a thin nitrogenated layer on the surface of the fine $Nd_2Fe_{14}B$-type particles, which enhanced the anisotropy field and gave improved resistance to oxidation (dissociation).

• Journal of Magnetics
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• 제15권4호
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• pp.169-172
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• 2010

The coercivity mechanism in permanent magnets was analyzed according to the effects of domain nucleation and domain wall pinning. The coercivity mechanism of a TbCo thin film with high perpendicular magnetic anisotropy was considered in terms of the local inhomogeneity in the thin film. The initial magnetization curves of the TbCo thin films demonstrated domain wall pinning to be the main contributor to the coercivity mechanism than domain nucleation. Based on the coercivity model proposed by Kronmuller et al., the inhomogeneity size acting as a domain wall pinning site was determined. Using the measured values of perpendicular anisotropy constant ($K_u$), saturation magnetization ($M_s$), and coercivity ($H_c$), the inhomogeneity size estimated in a TbCo thin film with high coercivity was approximately 9 nm.

• 한국분말재료학회지
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• 제23권6호
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• pp.432-436
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• 2016

We investigate the microstructural and magnetic property changes of $DyH_2$, $Cu+DyH_2$, and $Al+DyH_2$ diffusion-treated NdFeB sintered magnets with the post annealing (PA) temperature. The coercivity of all the diffusion-treated magnets increases with increasing heat treatment temperature except at $910^{\circ}C$, where it decreases slightly. Moreover, at $880^{\circ}C$, the coercivity increases by 3.8 kOe in Cu and 4.7 kOe in Al-mixed $DyH_2$-coated magnets, whereas this increase is relatively low (3.0 kOe) in the magnet coated with only $DyH_2$. Both Cu and Al have an almost similar effect on the coercivity improvement, particularly over the heat treatment temperature range of $790-880^{\circ}C$. The diffusivity and diffusion depth of Dy increases in those magnets that are treated with Cu or Al-mixed $DyH_2$, mainly because of the comparatively easy diffusion path provided by Cu and Al owing to their solubility in the Nd-rich grain boundary phase. The formation of a highly anisotropic $(Nd,\;Dy)_2Fe_{14}B$ phase layer, which acts as the shell in the core-shell-type structure so as to prevent the reverse domain movement, is the cause of enhanced coercivity of diffusion-treated Nd-Fe-B magnets.

• 한국분말재료학회지
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• 제21권4호
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• pp.256-259
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• 2014

A magnetic powder, M-type barium hexaferrite (BaFe12O19), was consolidated with the spark plasma sintering process. Three different holding temperatures, $850^{\circ}C$, $875^{\circ}C$ and $900^{\circ}C$ were applied to the spark plasma sintering process with the same holding times, heating rates and compaction pressure of 30 MPa. The relative density was measured simultaneously with spark plasma sintering and the convergent relative density after cooling was found to be proportional to the holding temperature. The full relative density was obtained at $900^{\circ}C$ and the total sintering time was only 33.3 min, which was much less than the conventional furnace sintering method. The higher holding temperature also led to the higher saturation magnetic moment (${\sigma}_s$) and the higher coercivity ($H_c$) in the vibrating sample magnetometer measurement. The saturation magnetic moment (${\sigma}_s$) and the coercivity ($H_c$) obtained at $900^{\circ}C$ were 56.3 emu/g and 541.5 Oe for each.

• Journal of Magnetics
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• 제4권4호
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• pp.131-135
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• 1999

The HDDR characteristics of the Nd-Fe-B-type isotropic and anisotropic HDDR alloys were investigated using three types of alloys: alloy A $(Nd_{12.6}Fe_{81.4}B_6), alloy B (Nd_{12.6}Fe_{81.3}B_6Zr_{0.1}), and alloy C (Nd_{12.6}Fe_{68.8}Co_{11.5}B_6Ga_{1.0}Zr_{0.1}$). The alloy A is featured with the isotropic HDDR character, while alloy B and C are featured with the anisotropic HDDR character. Hydrogenation and disproportionation characteristics of the alloys were examined using DTA under hydrogen gas. Recombination characteristics of the alloys were examined by observing the coercivity variation as a function of recombination time. The present study revealed that the alloy C exhibits slightly higher hydrogenation and disproportionation temperatures compared to the alloy A and B. Recombination of the anisotropic alloy B and C takes place more rapidly with respect to the isotropic alloy A. The intrinsic coercivities of the recombined materials rapidly increased with increasing the recombination time and then showed a peak, after which the coercivities decreased gradually. The degraded coercivity was, however, recovered significantly on prolonged recombination treatment. Compared with the isotropic HDDR alloy A the anisotropic HDDR alloy B and C are notable for their greater recovery of coercivity. The significant recovery of coercivity was accounted for the in terms of the development of well-defined smooth grain boundary between the recombined grains on prolonged recombination.

• Journal of Magnetics
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• 제21권2호
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• pp.235-238
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• 2016

Microstructure and magnetization behaviors of $MnBi/Fe_3B/Nd2_Fe_{14}B$ nanocomposite alloy have been investigated. It was found that the coercivity increased firstly and then decreased, and saturation magnetization decreased with the additon of MnBi alloy. The addition of 40 wt.% MnBi powder enhanced the coercivity from 192.8 kA/m to 311.2 kA/m. The ${\delta}M$ and D(H)-H plots suggested the occurrence of a stronger exchange-coupling occurring between the hard and soft magnetic phase for this sample. The dependence of coercivity with temperature was discussed in 40 wt.% $Mn_{55}Bi_{45}$/ 60 wt.% $Nd_{4.5}Fe_{76.5}Nb_{0.5}B_{18.5}$ alloy powder, and a positive temperature coefficient was founded from 298 K to 350 K.