• 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.

• Journal of Magnetics
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• v.18 no.3
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• pp.235-239
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• 2013

The effect of Dy addition on the microstructure and magnetic properties of the sintered NdFeB magnets was investigated. The results of the microstructure analysis showed that Dy-free and Dy-doped samples are composed of $Nd_2Fe_{14}B$ (P42/mnm) and a trace of Nd-rich phase. Dy addition reduces significantly the pole density factor of (004), (006) and (008) crystal faces as estimated by the Horta formula. Accordingly, the coercivity of the Dy-doped sample increases from 2038 $kA{\cdot}m^{-1}$ up to 2288 $kA{\cdot}m^{-1}$. The $H_{cj}(T)/M_s(T)$ versus $H^{min}_N/M_s(T)$ (Kronm$\ddot{u}$ller-plot) behavior shows that the nucleation is the dominating mechanism for the magnetization reversal in these two kinds of magnets, and two microstructural parameters of ${\alpha}_k$ and $N_{eff}$ are obtained. The Kronm$\ddot{u}$ller-Plot gives evidence for an increase of the ${\alpha}_k$ responsible for an increase of the coercivity as the result of the increase of the magnetic field as the magnetic domain reversed.

• Journal of Magnetics
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• v.15 no.1
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• pp.40-44
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• 2010

This paper introduces two types of magnetization, and reports the effect of the magnetization direction on the iron loss in a brushless DC (BLDC) motor using a 2-D time-stepped voltage source finite-element method (FEM). The iron losses were found to consist of hysteresis and eddy current loss, which were calculated from the time variation of the magnetic field distribution. To confirm the analysis, a prototype BLDC motor was constructed with a sintered ferrite magnet. The analysis and experimental results suggest that the magnetization direction has a significant effect in terms of the iron loss characteristics of the BLDC motor.

• Journal of the Korean Ceramic Society
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• v.42 no.10 s.281
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• pp.672-677
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• 2005

In this study we prepared the Sr-ferrite powders and magnet by a molten salt method using the (NaCl+KCl) salt mixture. Starting materials of $Fe_{2}$$O_{3}$ and Sr$Co_{3}$ were mixed as the molar ratio of 5.70:1, and 0.08 mol$ \% $ $Al_{2}$$O_{3}$, 0.10 mo1$ \% $ Si$O_{2}$ and 0.12 mo1$ \% $ CaO were added as additives. Sr-ferrite powders synthesized at the reaction temperatures of 800$\∼$1200$ ^{\circ}C $ showed the typical M-type hexagonal ferrite phase, and hexagonal plate-like morphology with uniform distribution of 1$\∼$3 $\mu$m particle size. The bulk density of the sintered Sr-ferrite magnet prepared with powders by the molten salt method showed the maximum density of 4.82 g/$cm^{3}$ at the sintering temperature of 1200$^{\circ}C $. The maxima of remanent flux density (Br, 45 emu/g) and coercive force (iHc, 3.75 kOe) occurred at the sintering temperatures of 1150$ ^{\circ}C$ and 1200$^{\circ}C $.

• Resources Recycling
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• v.12 no.6
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• pp.19-25
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• 2003

This experiment was carried out to examine the effect of iron oxide roasting for Sr-ferrite magnet. Chloride content was decreased with raising the 2 nd roasting temperature of iron oxide for ruthner process iron oxide. The optimization temperature for roasting of ruthner process iron oxide was around $800^{\circ}C$ as average particle size 1.5∼1.9 $\mu\textrm{m}$, apparent bulk density 1.4 g/$m\ell$ and chloride content 0.05%. The relation between Br and HcJ by sintering temperature for Sr-ferrite magnet was found to be Br≒-0.258HcJ＋494. In case of having a vibrating disk mill for the ruthner process iron oxide, the magnetic properties were Br 421 mT and HcJ 251 kA/m.

• Journal of the Korean Magnetics Society
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• v.22 no.6
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• pp.221-227
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• 2012

High performance permanent magnets have become the subject of considerable attention because of the potential applications in the traction motors of hybrid and electric vehicles and wind generators. Nd-Fe-B magnets have attracted considerable interest due to a large maximum energy product. However, Nd-Fe-B magnet cannot be used in high temperature (${\sim}200^{\circ}C$) applications due to the thermal degradation of coercivity. Therefore, the development of high coercivity Nd-Fe-B permanent magnet is a challenging issue. In case of high coercivity Nd-Fe-B permanent magnet, an increment in the intrinsic coercivity can be easily achieved by substituting Nd atoms with Dy or Tb atoms. However, these heavy rare-earth elements are known to cause a decrease in remanence due to the antiferromagnetic coupling between Dy and Fe atoms. In addition, Dy is relatively expensive and being limited in quantity. Hence, a new technology that can increase the coercivity of Nd-Fe-B sintered magnet using only a small amount, or even, no amount of heavy rare-earth elements is being investigated. This article describes the research trend in reducing the heavy rare-earth elements in Nd-Fe-B magnets.

• Proceedings of the Korean Magnestics Society Conference
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• 2003.12a
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• pp.214-214
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• 2003

• Proceedings of the Korean Magnestics Society Conference
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• 2007.05a
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• pp.184.1-184.1
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• 2007

• Proceedings of the Korean Magnestics Society Conference
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• 2014.05a
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• pp.35-35
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• 2014

• Proceedings of the Korean Magnestics Society Conference
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• 2014.05a
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• pp.82-83
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• 2014