• Journal of Industrial Technology
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• v.28 no.A
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• pp.119-123
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• 2008

Structural and magnetic properties of $CO_{1-x}Zn_xZ$ ($Ba_3Co_{1-x}Zn_xFe_{24}O_{41}$) hexa-ferrite are studied using XRD, VSM and SEM, respectively. Powder was prepared from co-precipitation and firstly heat treated at $1350^{\circ}C$ for 6 hours in $O_2$ atmosphere. Second heat treatment was performed at 900, 1000, $1100^{\circ}C$ for 6 hours in air, respectively. Saturation magnetization value of first heat treated powder is acceptable and coercivity is high for applying to device. These result may be originated from incomplete formation reaction from M and Y phases to Z phase. Second heat treatment leads to small value of coercivity.

• Journal of Magnetics
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• v.19 no.1
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• pp.5-9
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• 2014

The amine functionalized $CoFe_2O_4$ nanoparticles were prepared by thermal decomposition method at reflux temperatures $160^{\circ}C$ and $172^{\circ}C$. The obtained $CoFe_2O_4$ nanoparticles at $160^{\circ}C$ reflux temperature show aggregation free poly-dispersed nanoparticles in 4-15 nm range. In an elevated reflux temperature of $172^{\circ}C$, $CoFe_2O_4$ show aggregated poly-dispersed nanoparticles in the size range of 20-46 nm. The saturation magnetization value at 300 K exhibited 51 emu/g at reflux temperature of $160^{\circ}C$. However, the sample synthesized at an elevated temperature of $172^{\circ}C$ has shown a coercive field value of 560 Oe with saturation magnetization of 68 emu/g.

• Journal of the Korean Ceramic Society
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• v.32 no.4
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• pp.436-440
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• 1995

Effects of microstructure of two Mg-ferrite specimens with the same starting composition and relative density but with different grain size on B-H hysteresis loop, natural resonance frequency, and ferromagnetic resonance line width are reported. Such properties as B-H hysteresis loop, saturation magnetization, natural resonance frequency, and ferromagnetic resonance line width were influenced by the microstructure development during sintering. Large grain size specimen showed high saturation magnetization, low coercive force, low natural resonance frequency, and low ferromagnetic resonance line width compared with the specimen of small grain size. The main reason for the changes in properties can be explained by the variation in anisotropic characteristics due to Fe+2 content generated during sintering process.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.216-216
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• 2009

$(Ni_{1-x-y}Zn_xCu_y)Fe_2O_4(x=0.45,\;0{\leq}y{\leq}0.3)$ was synthesized by conventional ceramic processing, and the sintering behavior and the magnetic properties of which were studied as functions of CuO content and sintering temperature. Both the densification and the grain growth rates were significantly enhanced with the increase of CuO content, while abnormal grain growth occurred when the samples of $y{\geq}0.2$ were sintered above $950^{\circ}C$. Saturation magnetization and coercive field were mainly influenced by the densification and grain growth of the specimens, respectively.

• Journal of Powder Materials
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• v.9 no.5
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• pp.322-328
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• 2002

Fe-Co nanocomposite powders with different composition were prepared by chemical vapor condensation (CVC) process and their characterizations were studied by means of X-ray diffraction, transmission electron microscopy, and vibrating sample magnetometer. The particles having the mean size of 5~25 nm consisted of metallic cores and oxide shells. The Co contents and particle size increased with increasing the carrier gas flow rate of Co precursor. The saturation magnetization and coercivity increased with increasing Co content. and the saturation magnetization maximized at the 40 wt.%Co. The Fe-Co nanocomposite powder oxidized at $400^{\circ}C$ showed the maximum coercivity of 1739 Oe.

• Nuclear Engineering and Technology
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• v.29 no.5
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• pp.361-367
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• 1997

The phase separation in ferrite phase of duplex stainless steel is the primary cause of thermal aging embrittlement of the LWR primary pressure boundary components. In this study the phase separation of simulated duplex stainless steel was detected by Mossbauer spectroscopy and magnetic property analysis by VSM(Vibrating Specimen Magnetometer). The simulated duplex stainless steels, Fe-Cr binary, Fe-Cr-Ni ternary, and Fe-Cr-Ni-Si quarternary allots, were aged at 370 and 40$0^{\circ}C$ up to 5,340 hours. It was observed from Mossbauer spectra analysis that internal magnetic field increases with aging time and from VSM that the specific saturation magnetization and Curie temperature increase with aging time. These result are indicative that phase separation into Fe-rich region and Cr-rich region is caused by thermal aging in the temperature range of 370~40$0^{\circ}C$ In cases of specimens containing Ni, the increase of specific saturation magnetization is much higher. This implies that Ni seems to promote Fe-Cr interdiffusion, which accelerates the phase separation into Fe-rich $\alpha$ phase and Cr-rich $\alpha$' phase.

• Journal of the Korean Ceramic Society
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• v.34 no.4
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• pp.351-356
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• 1997

The origin of the variation of initial permeability in manganese-zinc ferrite polycrystals with a content of hematite was investigated. Initial permeability showed maximum with hematite content while there was no significant change in microstructure. Saturation magnetization increased with hematite content. So the variation of initial permeability was not explained on the basis of microstructural change or saturation magnetization. Temperature dependence of initial permeability revealed magnetocrystalline anisotropy was the origin of the variation of initial permeability. The change in magnetocrystalline anisotropy was ascribed to the variation in ferrous ion concentration. Therefore the variation of initial permeability in manganese-zinc ferrite polycrystals with a content of hematite was due to ferrous ion concentration via magnetocrystalline anisotropy.

• Journal of the Korean institute of surface engineering
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• v.44 no.6
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• pp.255-259
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• 2011

The thickness dependence of magnetic properties was experimentally investigated in nanocrystalline Fe-Hf-N thin films fabricated by a RF magnetron sputtering method. In order to investigate the thickness effect on their magnetic properties, the films are prepared with different thickness ranges from 90 nm to 330 nm. It was revealed that the coercivity of the thin film increased with film thickness. On the contrary, the saturation magnetization decreased with film thickness. On the basis of the SEM and TEM, an amorphous phase forms during initial growth stage and it changes to crystalline structure after heat treatment at $550^{\circ}C$. Nanocrystalline Fe-Hf-N particles are also generated.

• 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.

• 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.