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Young Rang Uhm,Sam Jin Kim,Chul Sung Kim 한국자기학회 2002 Journal of Magnetics Vol.7 No.1
The charge structures of La_(0.6)Sr_(0.4)FeO₃ (LSMO) and of the combined system (La_(0.6)Sr_(0.4)MnO₃)_(0.7)(La_(0.6)Sr_(0.4)FeO₃)_(0.3) are investigated by using Mossbauer spectroscopy. The antiferromagnetically ordered La_(0.6)Sr_(0.4)FeO₃(LSFO) has possible charges of Fe³+ and Fe⁴+, which include a low-spin Fe⁴+ state at and above 230 K. The temperature dependences of the Mossbauer spectra for the La_(0.6)Sr_(0.4)FeO₃ system and for the combined (LSMO)_(0.7)(LSFO)_(0.3) system are fitted as three sets of Zeeman patterns corresponding to Fe³+ and Fe⁴+ below 230 K. At and above 230 K, the fitted Mossbauer spectra for the combined system are the same in all temperature ranges. Above 230 K, La_(0.6)Sr_(0.4)FeO₃ spectrum consists of two sets of six Lorentzians for Fe³+ and one line for low spin Fe⁴+. It is worth noting that large fields are induced in the combined system.
Synthesis and Mossabuer Spectroscopy Studies of Nd₁-xBixY₂Fe5O₁₂ Nano - Particles
Young Rang Uhm,Jae-Gwang Lee,Chul Sung Kim 한국자기학회 2000 Journal of Magnetics Vol.5 No.1
The garnets Nd_(1-x)Bi_xY₂Fe_5O₁₂ (x=0.0, 0.25, 0.5, 0.75 and 1.0) have been studied by x-rays, electron microscopy, ferromagnetic resonance, vibrating sample magnetometer and Mossbauer spectroscopy. Ultra-fine polycrystalline cubic samples have been prepared by a melt-salt routed sol-gel method. The Mossbauer spectra consist of two sets of six-line patterns corresponding to Fe³+ at the tetrahedral 24(d) and octahedral 16(a) sites. Magnetic hyperfine fields of Nd_(0.5)Bi_(0.5)Y₂Fe_5O₁₂ at 12 K are found to be 548 kOe (octahedral site) and 475 kOe (tetrahedral site), respectively. It is found that Debye temperatures for the tetrahedral and octahedral sites of Nd_(0.75)Bi_(0.25)Y₂Fe_5O₁₂ are θtet=436 K and θoct=285 K, respectively. The iron ions at both sites are highly covalent ferric. The Neel temperature decreases linearly with Bi concentration, from 630 K for x=0.0 to 600 K for x=1.0, suggesting that the superexchange interaction for the Nd-O-Fe link is stronger than that for the Bi-O-Fe link. As a consequence, the coercivity of Nd_(1-x)Bi_xY₂Fe_5O₁₂ drastically decreases and the magnetization remains almost constant as x increases.
Provenance Studies for Prehistoric Obsidian by Using Mössbauer Spectroscopy
Uhm Young Rang,Sun Gwang-Min,Jin Mi-Eun,Jwa Yong-Joo,Seo Jae Yeon,Choi Hyunkyung,Kim Chul Sung 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.77 No.3
The iron compounds in minerals of obsidians from the continental Far East, Mount Baekdu (Baedusan) near the Sino-Korean border and Kyushu in southwest Japan were studied using 57Fe Mössbauer spectroscopy. The mineral Pyroxene (FeSiO3) in obsidian was found in the metamorphic rocks of Mount Beakdusan and Kyushu. However, the mineral biotite in obsidian was found in Kyushu only. The chemical compounds of the microlites in obsidians from Mount Baekdu are quite different from those in the Kyushu obsidians. The Mössbauer spectrum measured on the Baekdusan obsidian was fitted using two sextets, two ferrous iron doublets, and a ferric iron doublet tentatively assigned to clinopyroxene. Two sextets result from the nonstoichiometric magnetite. In contrast, Kyushu obsidians consisted of two sextets, a ferrous iron doublet for clinopyroxene, and a ferric iron doublet tentatively associated with biotite. In mineralogical and geochemical studies on the Baekdusan and Kyushu obsidians, the origination of the magma compositions and the crystallization environments were confirmed to have been different.
Effect of Fe Magnetic Nanoparticles in Rubber Matrix
Young Rang Uhm,Jaewoo Kim,Jiheon Jun,Sol Lee,Chang Kyu Rhee,Chul Sung Kim 한국자기학회 2010 Journal of Magnetics Vol.15 No.4
A new kind of magnetic rubber, Fe dispersed ethylene propylene monomer (EPM), was prepared by a conventional technique using a two roll mill. The magnetic fillers of Fe-nanoparicles were coated by low density polyethylene (LDPE). The purpose of surface treatment of nanoparticles by LDPE is to enhance wettability and lubricancy of the fillers in a polymer matrix. The mechanical strength and microstructure of the magnetic rubber were characterized by tensile strength test and scanning electron microscopy (SEM). Results revealed that the Fe nanoparticles were relatively well dispersed in an EPM matrix. It was found that the nano- Fe dispersed magnetic rubber showed higher coercivity and tensile strength than those of micron- Fe dispersed one.