• Proceedings of the Korean Magnestics Society Conference
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• 2004.12a
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• pp.231-232
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• 2004

• Proceedings of the Korean Magnestics Society Conference
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• 2001.10a
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• pp.98-98
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• 2001

• Journal of the Korean Magnetics Society
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• v.5 no.4
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• pp.281-286
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• 1995

In order to study the effect of additives $SiO_{2}$ on the magnetic properties of hexaferrite sheet magnet, we used X-ray diffractometer, Mossbauer spectrometer, and VSM magnetometer. We have prepared $Ba_{0.25}Sr_{0.75}Fe_{12}O_{19}$ green sheets by the Dr. Blade method. Most of samples have a magnetoplurnbite crystal structure of typical M-type hexaferrite. The lattice parameters are found not to be affected by the addition of $SiO_{2}$. ${\alpha}-Fe_{2}O_{3}$ phase develops above $SiO_{2}$ 2.0 wt.%. Isomer shifts indicate that the valence of Fe ions is trivalent. Curie temperatures decrease slightly with increasing $SiO_{2}$ concentrations. It means that the $Si^{4+}$ subsitution for 12k-site $Fe^{3+}$ has an effect on the superexchange interactions Fe-O-Fe, which change the distance and the angle between cations and anions. It was suggested that ${\alpha}-Fe_{2}O_{3}$ phase results from the excessive Fe produced by subsituting $Si^{4+}$ for $Fe^{3+}$. Based upon the results of $Ba_{0.25}Sr_{0.75}Fe_{12}O_{19}$ added with $SiO_{2}$, we concluded that $H_{c}$, $M_{s}$ and $M_{r}$ depend more strongly on the microstructure chracteristics than on the cation substitution.

• Proceedings of the Korean Magnestics Society Conference
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• 1998.10a
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• pp.64-65
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• 1998

• Journal of the Korean Magnetics Society
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• v.19 no.6
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• pp.216-221
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• 2009

Y-type barium ferrite $Ba_2Co_2Fe_{12}O_{22}$ was synthesized by a solid state reaction method. Effects of metal ion mole ratio and calcination temperatures on magnetic properties and microstructures of the synthesized powders were investigated. Phase analysis and microstructure observation were performed with a XRD (X-ray diffractometer) and a FESEM (field effect scanning electron microscope), respectively. Magnetic properties of the powders were measured with a VSM (vibrating sample magnetometer). Single phase Y-type was synthesized when metal ion mole fraction $Fe^{3+}:\;Ba^{2+}:\;Co^{2+}$ was 6 : 1 : 1 and calcination temperature was $1050\;{^{\circ}C}$. High saturation magnetization value of 39.1 emu/g was obtained when metal ion mole fraction $Fe^{3+}:\;Ba^{2+}:\;Co^{2+}$ was 8 : 1 : 1 and calcination temperature was $1200\;{^{\circ}C}$.

• Journal of the Korean Magnetics Society
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• v.9 no.1
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• pp.35-40
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• 1999

Sr substituted materials for some barium in M-type barium ferrite powder and Co-Ti substituted Sr-Ba hexagonal ferrite powder were prepared by citrate sol-gel method and 2 MOE sol-gel method these hexaferrite particles were reduced for 1hr in the hydrogen gas. The reduction temperatures were varied in the range of 250 $^{\circ}C$ to 500 $^{\circ}C$. X-ray diffraction patterns were measured using diffractometer with Cu $K_{\Alhpa}$ radiation. Mossbauer absorption spectra were measured with a constant acceleration spectrometer. We have focused on studying the origin of increasing $M_s$ by M$\"{o}$ssbauer spectroscopy. Ferrite particles which were sintered at 105$0^{\circ}C$ were found to be typical magnetoplumbite structure and single phase. XRD patterns with varying the reduction temperatures in $Sr_{0.5}Ba_{0.5}Fe_{10}O_{19}$ indicates ferrites particles become composite hexaferrites containing $\alpha$-Fe at T_{red}=350 \;$^{\circ}C$$. On the otherhand, it was found that $Co^{2+}$ ions and $Ti^{4+}$ ions in $Sr_{0.7}Ba_{0.3}Fe_{10}CoTiO_{19}$ prevent from changing $Fe^{3+}$ ions to $\alpha$-Fe during the $H_2$ reduction. Comparing Mossbauer results with XRD results, we have determined most of $\alpha$-Fe are reduced from $4f_{vi}$ sites and 12k sites of $Fe^{3+}$ ions. These $\alpha$-Fe phase bring the induced anisotropy and increase saturation magnetization $M_s$.TEX>.

• Journal of the Korean Ceramic Society
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• v.20 no.4
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• pp.340-346
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• 1983

The effect of aging coprecipitate obtained by the reaction of mixed solution 1.1 mol FeCl-0.1 mol $BaCl_2$ and 4.0 mol. NaOH-1.0 mol $K _2 CO_3$ on the synthesis process of Baferrite $(BaFe_{12}O_{19})$ was investigated by means of DTA, TGA, XRD and electron microscope. The no-aged coprecipitate seems to be the aggregate of amorphosus $Fe_3$ .$nH_2O$ and (1-X) $BaCO_3$.$xBa(OH)_2$, but the 30 days-aged to be composed of crystalline $Fe_2O_3H_2O$ and $BaCO_3$. The decomposition temperature of $BaCO_3$ in the coprecipitate increases from 400-$700^{\circ}C$ to 700-90$0^{\circ}C$ with increment of aging-time. In the no-aged coprecipitate Ba-ferrite is synthesized through the surface reaction of amorphous Fe_2O_3$ and skeleton crystal BaO at 800-90$0^{\circ}C$ with more compact crystalization. During calcination of the 30 days-aged coprecibitate the intermediate phase BaFe_2O_4$ is formed at 600-$700^{\circ}C$ and completely transformed to Ba-ferrite at 800-90$0^{\circ}C$.

• Journal of the Korean Magnetics Society
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• v.10 no.4
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• pp.154-158
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• 2000

Crystallographic and magnetic properties of the Co and Ti-doped BaF $e_{12-2x}$ $Co_{x}$ $Ti_{x}$ $O_{19}$(0.0$\leq$x$\leq$1.0) system have been investigated by means of x-ray diffractometry, Mossbauer spectroscopy, and vibrating sample magnetometer. The structure of the system was found to be the magnetoplumbite structure, and the lattice parameter a is nearly constant and c increase as the doped Co-Ti contents increasing. We found that the saturation magnetization nearly unchanged but the coercivity rapidly decreased between x = 0.0 and x = 0.2 with increasing x in BaF $e_{12-2x}$ $Co_{x}$ $Ti_{x}$ $O_{19}$. From the Mossbauer spectra analysis Co-Ti ions prefer 12k, 4 $f_{vi}$ and 2b sites.tes.

• Journal of the Korean Magnetics Society
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• v.20 no.4
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• pp.134-142
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• 2010

Barium ferrite ($BaFe_{12}O_{19}$) powders were synthesized by the co-precipitation method. $Fe^{3+}:Ba^{2+}$ mole ratio was fixed 8 and relative amount of $Fe^{3+}$ and $Ba^{2+}$ was controlled. The effects of the pH (= 8, 9, 10), calcination temperature and time on the morphology, structure and magnetic properties of the barium ferrite particles are characterized using XRD, FESEM, and VSM respectively. Coercivity and magnetization value of powders were changed with calcination temperature and time, relative amount of $Fe^{3+}$ and $Ba^{2+}$ and pH. Single-phase barium ferrite was obtained when pH value was 9 in the investigated range of $Fe^{3+}:Ba^{2+}$ relative amount and secondary phases were appeared at $Fe^{3+}:Ba^{2+}$ relative amount of 14.4 : 1.8. The largest value of magnetization (65.7 emu/g) was obtained when $Fe^{3+}:Ba^{2+}$ mole ratio was 12.8 : 1.6 and calcination temperature was $900^{\circ}C$ with air calcination atmosphere. The largest value of coercivity (5280 Oe) was obtained with $O_2$ calcination atmosphere.

• 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.