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Chepurnov S.A.,Chepurnova N.E.,Jin-Kyu Park,Redkozubova O.M.,Pravdukhina A.A.,Abbasova K.R.,Buzinova E.V.,Mirina A.A.,Chepurnova D.A.,Dubina A.A.,Pirogov U.A.,Curtis M.,Uva L. 고려인삼학회 2007 Journal of Ginseng Research Vol.31 No.3
Pharmacology of Korean Red ginseng gives us unique possibility to develop new class of antiepileptic drugs today and to improve one’s biological activity. The chemical structures of ginsenosides (GS) have some principal differences from well-known antiepileptic new generation drugs. The antiepileptic effect of GS was also demonstrated in all models of epilepsy in rats (young and adult), which have studied, in all models of epilepsy including status epilepticus (SE), induced by lithium - pilocarpine. In our experiments in rats new evidences on protective effects were exerted as a result of premedication by GS. Pre-treatment of several GS could induce decrease of the seizures severity and brain structural damage (by MRI), neuronal degeneration in hippocampus. Wave nature of severity of motor seizures during convulsive SE was observed during lithium-pilocarpine model of SE in rats (the first increase of seizures was 30 min after the beginning of SE and the second - 90 min after. The efficacy of treatment on SE by ginsenoside as expected was observed after no less 3 weeks by daily GS i.p. administration. It is blocked SE or significantly decrease the severity of seizures during SE. The implication of presented data is that combination of ginsenosides from Korean Red ginseng and ginseng cell culture Dan25 that could be applied for prevention of epileptical status development. However, a development of optimal ratio of different ginsenosides (Rb1 Rc, Rg, Rf,) should consummate in the new antiepileptic drug development.
TbxEr1−xNi5compounds: An ideal model system for competing Ising-XYanisotropy energies
Pirogov, A. N.,Park, J.-G.,Ermolenko, A. S.,Korolev, A. V.,Kuchin, A. G.,Lee, Seongsu,Choi, Y. N.,Park, Junghwan,Ranot, Mahipal,Yi, Junghwan,Gerasimov, E. G.,Dorofeev, Yu. A.,Vokhmyanin, A. P.,Podlesn American Physical Society 2009 Physical review. B, Condensed matter and materials Vol.79 No.17
Magnetism of ordered and disordered alloys of R<sub>2</sub>Fe<sub>14</sub>B (R=Nd, Er) type
Teplykh, A.E.,Chukalkin, Yu.G.,Lee, S.,Bogdanov, S.G.,Kudrevatykh, N.V.,Rosenfeld, E.V.,Skryabin, Yu.N.,Choi, Y.,Andreev, A.V.,Pirogov, A.N. Elsevier Sequoia 2013 Journal of alloys and compounds Vol.581 No.-
Magnetic susceptibility, magnetization and neutron diffraction measurements have been performed to study structure and magnetic states of crystalline and amorphous Nd<SUB>2</SUB>Fe<SUB>14</SUB>B and Er<SUB>2</SUB>Fe<SUB>14</SUB>B alloys. In the crystalline state there exists a large (about 20%) anisotropy of Er-sublattice magnetization. Values of the magnetic anisotropy constant of Er ions and the Er-Fe exchange-coupling parameter were estimated using temperature dependence of the Er- and Fe-sublattice magnetizations. Amorphous state of the samples was obtained by irradiation of fast (E<SUB>eff</SUB>≥1@?eV) neutrons with a fluence up to the 1.2x10<SUP>20</SUP>n/@?m<SUP>-2</SUP> at 340K. It is shown that antiferromagnetic coupling between the rare-earth and iron spins is kept in the amorphous state. Amorphization of the samples is found to result in reduction of the Curie temperature (T<SUB>C</SUB>) by about 200K and almost total absence of coercivity. We suggest that the strong decrease of T<SUB>C</SUB> is a consequence of enhancement of negative Fe-Fe interactions as a result of dispersion of interatomic distances, which is a characteristic feature of the amorphous state.
Giant magneto-elastic coupling in multiferroic hexagonal manganites
Lee, Seongsu,Pirogov, A.,Kang, Misun,Jang, Kwang-Hyun,Yonemura, M.,Kamiyama, T.,Cheong, S.-W.,Gozzo, F.,Shin, Namsoo,Kimura, H.,Noda, Y.,Park, J.-G. Nature Publishing Group 2008 Nature Vol.451 No.7180
The motion of atoms in a solid always responds to cooling or heating in a way that is consistent with the symmetry of the given space group of the solid to which they belong. When the atoms move, the electronic structure of the solid changes, leading to different physical properties. Therefore, the determination of where atoms are and what atoms do is a cornerstone of modern solid-state physics. However, experimental observations of atomic displacements measured as a function of temperature are very rare, because those displacements are, in almost all cases, exceedingly small. Here we show, using a combination of diffraction techniques, that the hexagonal manganites RMnO<SUB>3</SUB> (where R is a rare-earth element) undergo an isostructural transition with exceptionally large atomic displacements: two orders of magnitude larger than those seen in any other magnetic material, resulting in an unusually strong magneto-elastic coupling. We follow the exact atomic displacements of all the atoms in the unit cell as a function of temperature and find consistency with theoretical predictions based on group theories. We argue that this gigantic magneto-elastic coupling in RMnO<SUB>3</SUB> holds the key to the recently observed magneto-electric phenomenon in this intriguing class of materials.
Effects of magnetic anisotropy and exchange in Tm2Fe17
Pirogov, A. N.,Bogdanov, S. G.,Rosenfeld, E. V.,Park, J. -G.,Choi, Y. N.,Lee, Seongsu,Prokeš,, K.,Golosova, N. O.,Sashin, I. L.,Kudrevatykh, N. V.,Skryabin, Yu. N.,Vokhmyanin, A. P. Pleiades Publishing 2012 Journal of experimental and theoretical physics Vol.115 No.5
Determination of Texture Degree of NdFeB-Magnets by Means of Neutron Diffraction
Teplykh, A.E.,Bogdanov, S.G.,Choi, Yong,Kudrevatykh, Nikolai V.,Pirogov, A.N.,Popov, A.G.,Skryabin, Yu.N.,Vyatkin, V.P. Trans Tech Publications, Ltd. 2010 Diffusion and defect data. SSP. [Pt. B], Solid sta Vol.168 No.-
<P>Six samples of Nd-Fe-B-permanent magnets, distinguished in the texture degree, have been measured by neutron diffraction in the reflection and transmission regimes. The texture in the samples was formed by application of impulses of external magnetic field 0H = 4 T. Analysis of the obtained neutron diagrams by means of the Fullprof program allowed quantitative determination of the texture degree and conclusion to be made that the texture degree grows with an increase in numbers of magnetic field impulses.</P>
외부 자기장에 의한 Tb3Fe5O12의 자기스핀 재배열과 격자 변형
김정석(J. S. Kim),A. N. Pirogov,성백석(B. S. Sung) 호서대학교 공업기술연구소 2020 공업기술연구 논문집 Vol.39 No.2
Fe₅O₁₂ 에서 외부자기장 (μ₀H = 0, 0.8T)을 가해주면서 8.8K ~ 103K 온도 범위에서 중성자회절 실험을 하였다. 자기장에 의해 canted 자기스핀의 재배열과 격자의 변형을 분석하였다. magneto-dielectrric 효과는 magnetostriction이 아닌 spin-lattice coupling에 의해 발생하는 것으로 분석되었다. spin-lattice coupling은 Fe-Tb 결합길이 변화, 산소 octahedron 회전 등으로 인해 큰 magneto-dielectric effect △ε/ε를 일으킨다. The evolutions of lattice distortions along with the re-orientation of canted magnetic spins in the Tb₃Fe₅O₁₂ under external magnetic field μ₀H = 0.8T have been characterized by means of neutron diffraction over the temperature range 8.8K ~ 103K. Neutron data were collected from the pure polycrystalline Tb₃Fe₅O₁₂ sample at 8.8K, 65K, and 103K at zero field and at μ₀H = 0.8T. We suggest that the large magneto-dielectrric effect in Tb₃Fe₅O₁₂ originates from prominent spin-lattice coupling by external field: not from the magnetostriction produced by applying magnetic field. This spin-lattice coupling leads to the structural modifications such as, Fe-Tb bond distance, oxygen octahedron rotation, which give rises to a microscopic increase of ionic polarizability and a large magneto-dielectric effect △ε/ε in Tb₃Fe₅O₁₂.