• Journal of the Korean Magnetics Society
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• v.3 no.1
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• pp.34-40
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• 1993

Nylon 6 based magnetic pellets for injection molding were produced using plasma arc melt-spun $Nd_{10.5}Fe_{79}Co_{2}Zr_{1.5}B_{7}$ powders. Two sorts of bonded magnets made of two different sizes of particles ($38~75\;\mu\textrm{m}$ and $75~150\;\mu\textrm{m}$) were prepared to determine critical volume fraction of magnet powders, and the magnetic prop erties of the magnets were discussed as a function of density. For the nylon fi based Nd-Fe-Co-Zr-B pellets made of $38~75\;\mu\textrm{m}$ particles, the critical volume fraction of powders 0.7 was obtained with the pellet density which is 90% of theoretical density while the magnets of $75~150\;\mu\textrm{m}$ showed the density of 87% of the theoretical value with the same volume fraction. The nylon (i magnets with the addition of 0.5 wt. % silicon oil only exhibited the best magnetic properties to have $_{i}H_{c}=8.8\;kOe,\;B_{r}=5.1\;kG$ and $(BH)_{max}=5.2\;MGOe$ which are of world class. An empirical relationship in predicting the magnet density with a known fraction ($V_s$) of loading powders was obtained such as ${\rho}(g/cm^{3})=1.1+K.V_{s}$ where the K ranges over 5.3~5.6 be ing dependent upon the particle size loaded.

• Applied Chemistry for Engineering
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• v.10 no.3
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• pp.407-414
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• 1999

We have studied the reduction of NO by CO over perovskite-type oxides prepared by malic and method. The catalysts were modified to enhance the activity by substitution of metal into A or B site of perovskite oxides. In the $LaCoO_3$ type catalyst, the partial substitution of Sr into A site enhanced the catalytic activity on the conversion of NO at less than $350^{\circ}C$. In the $La_{0.6}Sr_{0.4}Co_{1-x}Fe_xO_3$ catalyst, the partial substitution of Fe or Mn into B site enhanced the conversion of NO, but excess amount of Fe decreased the conversion of NO. In addition, $La_{0.6}Sr_{0.4}Co_{0.8}Fe_{0.2}O_3$ mixed with $SnO_2$ or $MnO_2$ showed the synergy effect on the reduction of NO. The introduction of water into reactants feed decreased the catalytic activity but the deactivation was shown to be reversible. The introduction of $SO_2$ into reactants feed also decreased the catalytic activity.

• Korean Journal of Materials Research
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• v.28 no.7
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• pp.371-375
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• 2018

The manganese-, nickel-, and aluminum-doped cobalt ferrite powders, $Mn_{0.2}Co_{0.8}Fe_2O_4$, $Ni_{0.2}Co_{0.8}Fe_2O_4$, and $Al_{0.2}CoFe_{1.8}O_4$, are fabricated by the sol-gel method, and the crystallographic and magnetic properties of the powders are studied in comparison with those of $CoFe_2O_4$. All the ferrite powders are nano-sized and have a single spinel structure with the lattice constant increasing in $Mn_{0.2}Co_{0.8}Fe_2O_4$ but decreasing in $Ni_{0.2}Co_{0.8}Fe_2O_4$ and $Al_{0.2}CoFe_{1.8}O_4$. All the $M{\ddot{o}}ssbauer$ spectra are fitted as a superposition of two Zeeman sextets due to the tetrahedral and octahedral sites of the $Fe^{3+}$ ions. The values of the magnetic hyperfine fields of $Ni_{0.2}Co_{0.8}Fe_2O_4$ are somewhat increased in the A and B sites, while those of $Mn_{0.2}Co_{0.8}Fe_2O_4$ and $Al_{0.2}CoFe_{1.8}O_4$ are decreased. The variation of $M{\ddot{o}}ssbauer$ parameters is explained using the cation distribution equation, superexchange interaction and particle size. The hysteresis curves of the ferrite powders reveal a typical soft ferrite pattern. The variation in the values of saturation magnetization and coercivity are explained in terms of the site distributions, particle sizes and the spin magnetic moments of the doped ions.

• Proceedings of the Korean Magnestics Society Conference
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• 2011.06a
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• pp.161-162
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• 2011

• Journal of the Korean Chemical Society
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• v.27 no.3
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• pp.224-232
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• 1983

The effects of ball-milling time on solid state reactions in the system $BaCO_3-Fe_2O_3$ and the magnetic properties of Ba-ferrite 4(BaFe_{12}O_{19})$ have been studied. $BaCO_3-Fe_2O_3 $mixtures were prepared by ball-milling for varying lengths of time; 5, 15, 30, 80 and 200 hours. Techniques employed were thermogravimetry, X-ray diffraction analysis, scanning electron microscopy and B-H curve tracer. It is shown that the aggregation states and superparamagnetic size fractions obtained by increasing ball-milling time have remarkable effects on solid state reactions and magnetic properties of Ba-ferrite.

• Proceedings of the Materials Research Society of Korea Conference
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• 1995.11a
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• pp.58-58
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• 1995

• Proceedings of the KIEE Conference
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• 2001.10a
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• pp.27-29
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• 2001

In this paper, we study in magnetizing the NdFeB magnet which is inserted in a squirrel cage rotor. The inserted NdFeB magnet need much more magnetizing flux than that of ferrite magnet. Also the eddy current flowing in rotor bar disturbs the magnetizer in magnetizing the NdFeB magnet. The existing magnetizing yoke is designed by increasing the coil turn. But we recognize that only by increasing the coil turn it is impossible to make NdFeB magnet magnetized fully. Hence, in this paper we propose the method of increasing magnetizing flux by reducing the rotor bar area.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.702-709
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• 1995

In this paper we review recent work in our laboratory on nanocomposite CoSm-based films including CoSm with Cr underlayer (CoSm//Cr), exchange-coupled magnetic films consisting of CoSm and FeCo layers (CoSm/FeCo), and CoSm multilayers with nonmagnetic spacing layers of SmO (CoSm/SmO). The emphasis is on detailed investigations of microstructure and magnetic properties for CoSm//Cr films, exchange-spring effects for CoSm/FeCo films, and interlayer effects for (CoSm/ SmO) multilayers.

• Journal of Sensor Science and Technology
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• v.17 no.3
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• pp.203-209
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• 2008

Thick film formaldehyde (HCHO) gas sensors were fabricated by using $La_1_{-x}Sr_xMO_3$ (M= Fe, Co, Mn) ceramics. The powders of $La_1_{-x}Sr_xMO_3$ (M=Fe, Co, Mn) were synthesized by conventional solid-state reaction method. By using the $La_1_{-x}Sr_xMO_3$ (M=Fe, Co, Mn) paste, the thick-film formaldehyde sensors were prepared on the alumina substrate by silkscreen printing method. The experimental results revealed that $La_1_{-x}Sr_xMO_3$ (M= Fe, Co, Mn) ceramic powder has a perovskite structure and the thick-film sensor shows excellent gas-sensing characteristics to formaldehyde gas (sensitivity of $La_{0.8}Sr_{0.2}FeO_3$, S= 14.7 at operating temperature of $150^{\circ}C$ in 50 ppm HCHO ambient).

• Journal of Magnetics
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• v.9 no.2
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• pp.40-46
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• 2004

The magnetic properties of sputtered ($Ni_{83}Fe_{17}/Au/Co/Au$) multilayers with various thicknesses of Au (0.5 {\leq} t_{Au} {\leq} 3 nm), Ni-Fe ($1{\leq}t_{Ni-Fe}{\leq}4nm$) and Co ($0.2{\leq}t_{co}{\leq}1.5nm$) layers were characterized. An alternating in-plane and out-of-plane anisotropy of the ferromagnetic layers was achieved for the structures ($t_{Au}{\geq}1.5nm$) showing a weak coupling between the Ni-Fe layers with an in-plane anisotropy and the Co layers ($0.3{\leq}t_Co{\leq}1.2nm$) with a perpendicular anisotropy. For such a structure, a detailed discussion on the GMR effect is presented, relating to the magnetization reversal from a mutually perpendicular magnetic configuration at the remanence to a parallel one at the saturation. An influence of the dense labyrinth domain structure on the magnetoresistance effect is also addressed.