• Journal of the Korean Ceramic Society
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• v.40 no.1
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• pp.62-68
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• 2003

Ba-ferrite particles added with Co and Ti, which were known well the additives for the control in coercivity, were synthesized by sol-gel method. In the range 90 to 120 minute reaction time, a stable sol solution which showed no change with temperature, pH, viscosity and aging time. After dried and heat treatment of sol solution, Ba-ferrite phase formed at $700^{\circ}C$ with Differential Thermal Analysis(DTA) and X-Ray Diffractometer(XRD) measurement. The crystallinity became to be better with increasing the temperature. It were showed by Scanning Electron Microscopy(SEM) that Ba-ferrite increased to particle sizes as increasing heating temperature and obtained of narrow particles size distribution. Also, magnetic characteristics of Ba-ferrite powders Co and Ti added were observed by a Vibrating Sample Magnetometer(VSM). Saturation magnetization$(M_s)$ was not much changed, however. the coercivity$(H_c)$dramatically dropped with addition of Co and Ti.

• Journal of Magnetics
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• v.18 no.4
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• pp.400-404
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• 2013

Grain boundary diffusion technique with $DyH_3$ nanoparticles was applied to fabricate Dy-less sintered Nd-Fe-B permanent magnets with high coercivity. The magnetic properties and microstructure of magnets were systematically studied. The coercivity and remanence of grain boundary diffusion magnet were improved by 60% and reduced by 7% compared with those of the original magnet, respectively. Meanwhile, both the remanence temperature coefficient (${\alpha}$) and the coercivity temperature coefficient (${\beta}$) of the magnets were improved after diffusion treatment. Investigation shows that Dy is preferentially enriched as (Nd, Dy)$_2Fe_{14}B$ phase in the surface region of the $Nd_2Fe_{14}B$ matrix grains indicated by the remarkable enhancement of the magneto-crystalline anisotropy field of the magnet. As a result, the magnet diffused with a small amount of Dy nanoparticles possesses enhanced coercivity without remarkably sacrificing its magnetization.

• Journal of Magnetics
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• v.14 no.1
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• pp.27-30
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• 2009

Various sintered magnets containing $28{\sim}31\;wt%$ Nd and $0{\sim}7\;wt%$ Dy were evaluated for coercivity and irreversible flux loss as a preliminary study to develop highly-coercive, high-temperature magnets that can be applied for driving motors in a hybrid vehicle. The sintered magnets were prepared in sequence of strip casting, HD treatment, jet milling, magnetic field pressing, sintering and post-annealing. Increasing Dy content and adjusting post-annealing temperature monotonically increased coercivity of magnets from about 14 kOe to 30 kOe. A magnet containing 28 wt% Nd and 7 wt% Dy exhibits a $(BH)_{max}$+$_i{H_c}$ value of almost 64. This is very close to what the automobile industry considers as the minimum value (65) for a hybrid vehicle system. Moreover, irreversible flux loss of the magnet was about 3% at $200^{\circ}C$, which is well less than the allowable limit (5%) to a driving motor in hybrid vehicles.

• Journal of Magnetics
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• v.12 no.1
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• pp.45-48
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• 2007

[ $Co_{100-X}Zr_X$ ] (x=10-40) alloys were prepared by using a mechanical alloying technique. Phase constitution of the crystallised material depended on the annealing temperature. The $Co_{82}Zr_{18}$ alloy crystallised at lower temperature around $550^{\circ}C$ consisted of $Co_{23}Zr_6$, $Co_5Zr$ and fcc-Co phases, while the alloy crystallised at higher temperature around $800^{\circ}C$ consisted of $Co_{23}Zr_6$ and fcc-Co phases. Phase constitution of the crystallised material also depended on the chemical composition of the alloy. The material with lower Zr content less than 10 at% Zr consisted of $Co_{23}Zr_6$ and fcc-Co, and the material with higher Zr-content over 30 at% consisted of $Co_2Zr$ phase. The material containing 15-20 at% Zr consisted of $Co_{23}Zr_6$, $Co_5Zr$ and fcc-Co. Only the material containing $Co_5Zr$ phase exhibited substantial coercivity, and it was confirmed that coercivity in the mechanically alloyed Co-Zr alloy was originated from the $Co_5Zr$ phase.

• Proceedings of the Korean Magnestics Society Conference
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• 1999.10a
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• pp.16-17
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• 1999

• Proceedings of the Korean Magnestics Society Conference
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• 1991.05a
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• pp.47-48
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• 1991

• Proceedings of the Korean Magnestics Society Conference
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• 2005.06a
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• pp.158-159
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• 2005

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1992.11a
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• pp.7-10
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• 1992

CoNiCr/Cr and CoCrTa/Cr for longitudinal magnetic recording media were. prepared on Coming 7059 glass by RF magnetron sputtering. The thickness of Cr underlayer was varied from 500 to $3000{\AA}$ and. that of magnetic layer was $700{\AA}$. Coercivity and squareness were measured using V.S.M.(vibrating sample magnetometer). The coercivity of films increased with increasing Cr thickness when the films were unannealed. The coercivity of the films annealed in a 10 mtorr vacuum increased initially with annealing time and then saturated with further increase in annealing time. The coercivity value difference between the unannealed and annealed films increased with increasing the thickness of Cr underlayer No significant change was found in squareness after anneal, regardless of Cr underlayer thickness.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11b
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• pp.77-80
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• 2001

Crystallographic and magnetic characteristics of CoCr-based magnetic thin film for perpendicular magnetic recording media were influenced on preparing conditions. In these, there is that substrate temperature was parameter that increases perpendicular coercivity of CoCrTa magnetic layer using recording layer. While preparation of CoCr-based doublelayer, by optimizing substrate temperature, we expect to increase perpendicular anisotropy of CoCr magnetic layer and prepare ferromagnetic recording layer with a good quality by epitaxial growth. CoCrTa/Si doublelayer showed a good dispersion angle of c-axis orientation $\Delta\theta_{50}$ caused by inserting amorphous Si underlayer which prepared at underlayer substrate temperature 250C. Perpendicular coercivity was constant, in-plane coercivity was controlled a low value about 200Oe. This result implied that Si underlayer could restrain growth of initial layer of CoCrTa thin film, which showed bad magnetic properties effectively without participating magnetization patterns of magnetic layer. In case of CoCrTa/Si that prepared with ultra thin underlayer, crystalline orientation of CoCrTa was improved rather underlayer thickness 1nm, it was expected that amorphous Si layer played a important role in not only underlayer but also seed layer.

• Journal of Powder Materials
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• v.16 no.4
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• pp.285-290
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• 2009

HDDR treated anisotropic Nd-Fe-B powders have been widely used, due to their excellent magnetic properties, especially for sheet motors and sunroof motors of hybrid and electric vehicles. Final microstructure and coercivity of such Nd-Fe-B powders depend on the state of starting mother alloys, so additional homogenization treatment is required for improving magnetic properties of them. In this study, a homogenization treatment was performed at $900\sim1140^{\circ}C$ in order to control the grain size and Nd-rich phase distribution, and at the same time to improve coercivity of the HDDR treated magnetic powders. FE-SEM was used for observing grain size of the HDDR treated powder and EPMA was employed to observe distribution of Nd-rich phase. Magnetic properties were analyzed with a vibrating sample magnetometer.