• Journal of the Korean Magnetics Society
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• v.13 no.6
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• pp.226-230
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• 2003

In this study, we analyzed the volcanic rock and scoria samples taken from special sites of Jeju island in two ways at the room temperature. One is the analysis of the chemical composition using X-ray fluorescence spectrometer, the other is the analysis of minerals in the samples, oxidized iron's genus, valence state and magnetic properties using X-ray diffractometry and Mossbauer spectroscopy. We believe that the volcanic rock and scoria samples are chiefly made of silicate minerals, like SiO$_2$, and they also have olivine, pyroxene, ilmenite, hematite and magnetite. The major Fe fractions of the volcanic rock samples are 2+ charge state and those of the scoria samples are 3+ charge state.

• Journal of the Korean Magnetics Society
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• v.8 no.4
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• pp.198-202
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• 1998

We have studied $Al_xFe_{3-x}O_4$ produced by direct composition method using X-ray diffraction and Mssbauer spectroscopy. The cation distribution for $Al_xFe_{3-x}O_4$ was determined by the ratio of sub-spectra absorption area. The charge state of Fe atoms in octahedral site(B-site) is $Fe^{2.5+}$ based on electron hopping, $Fe^{2+}$ ↔ $(Fe^{3+},Al^{3+})$ without dependency of substituted Al amounts.

• Journal of the Korean Magnetics Society
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• v.19 no.6
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• pp.227-232
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• 2009

Fe compounds of scoria samples distributed in the western seaside area of Jeju island were investigated by means of X-ray fluorescence spectroscopy (XRD), X-ray diffractometry (XRF) and $^{57}Fe$ Mossbauer spectroscopy. The samples were prepared from five parasite volcanos. We found that the samples were a typical basalt from the contents ratio of $SiO_2,\;Al_2O_3$ and Fe, and that they were silicate minerals. Underwater volcanoes scoria samples are shown only doublets in Mossbauer spectra and others scoria samples are shown sextets due to hematite and magnetite. And the balence state of Fe in the underwater volcanoes scoria samples are chiefly 2+ charge state with a little of the 2+ charge state. But the balence state of Fe in the others scoria samples are chiefly 3+ charge state.

• Korean Journal of Materials Research
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• v.9 no.7
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• pp.701-706
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• 1999

The crystal structure and magnetic properties of magnetic oxide system (F $e_2$ $O_3$)$_{5}$(A $l_2$ $O_3$)$_{4-x}$(G $a_2$ $O_3$)$_{x}$)SiO has been studied using X-ray diffraction and Mossbauer spectroscopy The changes of magnetic structure by the Ga ion substitution and the temperature variation have been investigated using Mossbauer spectroscopy, and the results are compared with those of the SQUIB measurements. Results of X-ray diffraction indicated that the crystal structures of the system change from a cubic spinel type to an orthorhombic via the intermediate region. This magnetic oxide system seems to be new kind of spinel type ferrites containing high concentration of cation vacancies. Various and complicated Mossbauer spectra were observed in the samples (x>0.2) at temperatures lower than room temperature. This result could be explained by freezing of the superparamagnetic dusters. On cooling and substitution, magnetic states of the system show various and multicritical properties. Unexpected dip in magnetization curves below 50K was observed in SQUID measurements. It was interpreted as an effect of spin canting including spin freezing or collective spin behavior.ior.r.

• Journal of the Korean Magnetics Society
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• v.12 no.1
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• pp.7-13
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• 2002

The studies of non-figure plain coarse pottery from Jeju island is very important because it can explain the characters of plain coarse potteries of the bronze age and the early iron age. In this study, We analyzed the non-figure plain coarse popery from Jeju island in two ways. One is analysis of the chemical composition using X-ray fluorescence spectrometer and X-ray diffraction, the other is analysts of clay mineral contained iron, oxidized iron's genus, valence state and magnetic properties using Mossbauer spectroscopy. We confidence that non-figure plain coarse pottery is chiefly made of silicate minerals, like SiO$_2$. The content of noncrystalline ferrihydrite is supposed to be below 5-10 wt%, non-figure plain coarse pottery is considered to partly consist of Jeju island clay, which is made of neutral volcanic rock and the valence state of iron is Fe$\^$2+/ and Fe$\^$3+/. We presume the reason that the magnetic hyperfine field is lower than that of pure goethite is the change of crystal structure which transforms the combination states of Fe ions while the clay is being fired.

• Journal of the Korean Magnetics Society
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• v.12 no.1
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• pp.1-6
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• 2002

Al$\^$3+/ substituted garnet Y$_3$Fe$\_$5-x/Al$\_$x/O$\_$12/ (x=0.0, 0.25, 0.5, 0.75, 1.0) was fabricated by sol-gel method. The crystallographic and magnetic properties of Y$_3$Fe$\_$5-x/Al$\_$x/O$\_$12/ have been studied with Mossbauer spectroscopy, x-ray diffraction (XRD), thermogravimetry analysis (TGA), differential thermal analysis (DTA), and vibrating samples magnetometer (VSM). The crystal structure of Y$_3$Fe$\_$5/O$\_$12/ is found to be a cubic with the lattice constant a$\_$0/= 12.381$\pm$0.005 $\AA$. The lattice constants a$\_$0/ decreases linearly from 12.381 to 12.304 A as the Al concentration (x) increases from x=0.0 to 1.0. Mossbauer spectra of measured at Y$_3$Fe$\_$5-x/A1$\_$x/O$\_$12/ various absorber temperatures of 13 to 600 K. Mossbauer spectrum for x = 0.0 is consist of well resolved two sets of six line patterns. While with increasing Al concentration outer sextet patters, which is originating from octahedral sites, broadens widely. These phenomena are interpreted in terms of random probability distributions of Fe$\^$3+/ and Al$\^$3+/ in tetrahedral site.

• Journal of the Korean Chemical Society
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• v.38 no.12
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• pp.873-879
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• 1994

A series of samples of solid solutions in the $Sr_xEu_{1-x}FeO_{3-y}(0.00{\leq}x{\leq}1.00)$ system has been prepared at $1200^{\circ}C$ under an atmospheric air pressure. The structures of solid solutions are studied by X-ray diffraction, thermal, Mohr salt, and Mossbauer spectroscopic analyses. Their physical properties are also discussed with the electrical conductivities. X-ray diffraction data for the compositions of x = 0.00, 0.25, and 1.00 are assigned to the orthorhombic and the compositions of x = 0.50 and 0.75 to the cubic systems. The lattice volume reduced to cubic cell increases with the x value. The mole ratio of $Fe^{4+}$ iometric chemical formulas of the system are formulated from the x, $\tau$, and y values. The mixed valency state of Fe ions, the oxygen coordination, and covalent bond character are discussed with the Mossbauer spectroscopic data. The activation enegy of the electrical conductivities depends on the $\tau$ value in the temperature range of -$100^{\circ}C$ to $600\circC$ under the air pressure. The Mossbauer spectrum and electrical conductivity of the solid solutions are discussed with nonstoichiometric chemical compositions.

• Journal of the Korean Magnetics Society
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• v.10 no.2
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• pp.74-80
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• 2000

CoCr$_{x}$ Fe$_{2-x}$O$_4$(0.0$\leq$x$\leq$1.0) ferrites have been fabricated by sol-gel method. The crystallographic and magnetic properties of the samples were investigated by means of x-ray diffraction, scanning electron microscophy, Mossbauer spectroscopy and vibrating sample magnetometry. The structure of all the samples is cubic spinel type and the lattice constant decrease with increasing Cr content. The substituted Cr ions were located only in the B-site. The particle size also decreases with increasing Cr content. The Mossbauer spectra consist of two sextets due to Fe$^{3+}$ions at A- and B sites for 0.0$\leq$x$\leq$0.6, while, a paramagnetic doublet appears for 0.8$\leq$x$\leq$1.0. The magnetic hyperfine field decreases with increasing Cr content. The relaxation spectra was shown at 0.8$\leq$x$\leq$1.0 in CoCr$_{x}$ Fe$_{2-x}$O$_4$. The coercivity decreases drastically, while, the saturation magnetization decreases linearly with increasing x.ing x.

• Journal of the Korean Magnetics Society
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• v.13 no.6
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• pp.231-236
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• 2003

The $Al_{0.2}$CoF $e_{1.8}$ $O_4$ferrite powders have been prepared by the sol-gel method. The crystallographic and magnetic properties of the sample depending on annealing temperature have been investigated by means of x-ray diffraction, FE SEM, Mossbauer spetroscopy and vibrating sample magnetometry. The x-ray diffractions of all samples annealing temperature above 873 K clearly indicate the presence of spinel structure, the lattice constant decrease from 8.425 $\AA$ at 873 K to 8.321 $\AA$ at 1073 K, whereas the particle size rapidly increase from about 39 nm at 673 K to about 108 nm at 1073 K. The Mossbauer spectra annealed above 873 K could be fitted as the superposition of two sextets due to F $e^{3+}$ at A-site and B-site. The isomer shift (IS) and quadruple splitting (QS) values nearly constant with annealing temperature, whereas magnetic hyperfine field ( $H_{hf}$) of A-site slowly in crease and that of B-site fastly increases with increasing annealing temperature. The magnetic behaviour of powders shows that the saturation magnetization increase from 0.7 emu/g at 473 K to 72.1 emu/g at 1073 K while the coercivity decrease from 0.951 kOe at 673 K to 0.374 kOe at 1073 K with increasing annealing temperature.

• Proceedings of the Korean Magnestics Society Conference
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• 2002.04a
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• pp.92-93
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• 2002