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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
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
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.
Lee, Sang-Heon,Choi, Yong,Pirogov, Alexander American Scientific Publishers 2011 Journal of Nanoscience and Nanotechnology Vol.11 No.1
<P>Nano-sized Cu(x)Ni(x)Zn(1-x-y)Fe2O4 ferrites were prepared by using self-propagating high-temperature synthesis (SHS) and mechanical ball milling. As oxygen pressure increases and copper content decreases in the initial composition, average combustion temperature and combustion velocity increases in the ranges of 947 to 1150 degrees C and 4.2 to 6.5 mm/sec, respectively. The SHS products were agglomerated crystalline powders in which fine particles were present. The average particle of the pulverized SHS product was about 200 nm. Lattice parameters determined by neutron diffractometry are 8.4125 angstroms for Ni0.38Zn0.62Fe2O4 and a = 8.3540 angstroms for Cu0.29Ni0.28Zn0.43Fe2O4.</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.