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Proximity Effect for Asymmetrical Three-layered F/S Structures in External Magnetic Field
Maxim V. Avdeev,Sergey L. Tsarevskii,Yurii N. Proshin 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
We study the critical temperature Tc of the three-layered ferromagnet/superconductor (F/S)structures in the external magnetic field H parallel to the film. For the F1/S/F2 and F1/F2/Sasymmetrical trilayers, the triplet superconducting component is generated at noncollinear magnetizationsof the F layers. Assuming that all S and F layers are dirty, we solve boundary problem forthe Usadel function. The results of numerical calculations for Tc as function thicknesses both F1and F2 layers at various parameters F/S structure are presented. The application to the spin-switchproblem is discussed. We found that asymmetry can essentially change the spin-switch observationcondition. The re-entrant superconductivity caused by external magnetic field is predicted for theF1/F2/S trilayer.
LiTa<sub>2</sub>PO<sub>8</sub>: a fast lithium-ion conductor with new framework structure
Kim, Jaegyeom,Kim, Juhyun,Avdeev, Maxim,Yun, Hoseop,Kim, Seung-Joo The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.45
<P>A new lithium-ion conducting oxide, LiTa2PO8, with a three-dimensional (3D) framework structure was synthesized. The complementary use of synchrotron XRD and neutron diffraction revealed that LiTa2PO8 crystallized into a monoclinic system (space group <I>C</I>2/<I>c</I>) with lattice parameters <I>a</I> ≈ 9.716 Å, <I>b</I> ≈ 11.536 Å, <I>c</I> ≈ 10.697 Å, and <I>β</I> = 90.04°. In this structure, the TaO6 octahedra and PO4 tetrahedra are connected <I>via</I> corner-sharing to form an unprecedented anionic framework, [(TaO6/2)2(PO4/2)]<SUP>−</SUP>, providing a 3D pathway for lithium-ion conduction. The sintered LiTa2PO8 pellets exhibited excellent lithium-ion conductivities: bulk conductivity of 1.6 × 10<SUP>−3</SUP> S cm<SUP>−1</SUP> and total conductivity of 2.5 × 10<SUP>−4</SUP> S cm<SUP>−1</SUP> at 25 °C.</P>
Moon, Keon Ho,Avdeev, Maxim,Kim, Young-Il Academic Press 2017 Journal of solid state chemistry Vol.254 No.-
<P><B>Abstract</B></P> <P>Oxynitride type complex perovskites AM<SUB>0.2</SUB>Nb<SUB>0.8</SUB>O<SUB>3−<I>x</I> </SUB>N<SUB> <I>x</I> </SUB> (A = Sr, Ba; M = Li, Na, Mg) were newly synthesized by the solid state diffusion of Li<SUP>+</SUP>, Na<SUP>+</SUP>, or Mg<SUP>2+</SUP> into the layered oxide, A<SUB>5</SUB>Nb<SUB>4</SUB>O<SUB>15</SUB>, with concurrent O/N substitution. Neutron and synchrotron X-ray Rietveld refinement showed that SrLi<SUB>0.2</SUB>Nb<SUB>0.8</SUB>O<SUB>2.8</SUB>N<SUB>0.2</SUB>, SrNa<SUB>0.2</SUB>Nb<SUB>0.8</SUB>O<SUB>2.8</SUB>N<SUB>0.2</SUB>, and SrMg<SUB>0.2</SUB>Nb<SUB>0.8</SUB>O<SUB>2.6</SUB>N<SUB>0.4</SUB> had body-centered tetragonal symmetry (<I>I</I>4/<I>mcm</I>), while those with A = Ba had simple cubic symmetry (<I>Pm</I> 3 ̅ <I>m</I>). In the tetragonal Sr-compounds, the nitrogen atoms were localized on the <I>c</I>-axial 4<I>a</I> site. However, the octahedral cations, M/Nb (M = Li, Na, Mg) were distributed randomly in all six compounds. The lattice volume of AM<SUB>0.2</SUB>Nb<SUB>0.8</SUB>O<SUB>3−<I>x</I> </SUB>N<SUB> <I>x</I> </SUB> was dependent on various factors including the type of A and the electronegativity of M. Compared to the simple perovskites, ANbO<SUB>2</SUB>N (A = Sr, Ba), AM<SUB>0.2</SUB>Nb<SUB>0.8</SUB>O<SUB>3−<I>x</I> </SUB>N<SUB> <I>x</I> </SUB> had wider band gaps (1.76–2.15eV for A = Sr and 1.65–2.10eV for A = Ba), but significantly lower sub-gap absorption.</P> <P><B>Graphical abstract</B></P> <P>New complex perovskite oxynitrides AM<SUB>0.2</SUB>Nb<SUB>0.8</SUB>O<SUB>3−<I>x</I> </SUB>N<SUB> <I>x</I> </SUB> (A = Sr, Ba; M = Li, Na, Mg; <I>x</I> = 0.2, 0.4) were prepared via 2D → 3D lattice conversion of the hexagonal layered perovskite oxides.</P> <P>[DISPLAY OMISSION]</P>
3d -electron Heisenberg pyrochlore Mn2Sb2O7
Peets, Darren C.,Sim, Hasung,Avdeev, Maxim,Park, Je-Geun American Physical Society 2016 Physical Review B Vol.94 No.17
<P>In frustrated magnetic systems, geometric constraints or the competition among interactions introduce extremely high degeneracy and prevent the system from readily selecting a low-temperature ground state. The most frustrated known spin arrangement is on the pyrochlore lattice, but nearly all magnetic pyrochlores have unquenched orbital angular momenta, constraining the spin directions through spin-orbit coupling. Pyrochlore Mn2Sb2O7 is an extremely rare Heisenberg pyrochlore system with directionally unconstrained spins and low chemical disorder. We show that it undergoes a spin-glass transition at 5.5 K, which is suppressed by disorder arising from Mn vacancies, indicating this ground state to be a direct consequence of the spins' interactions. The striking similarities to 3d transition-metal pyrochlores with unquenched angular momenta suggests that the low spin-orbit coupling in the 3d block makes Heisenberg pyrochlores far more accessible than previously imagined.</P>
Yahia, H.B.,Essehli, R.,Avdeev, M.,Park, J.B.,Sun, Y.K.,Al-Maadeed, M.A.,Belharouak, I. Academic Press 2016 Journal of solid state chemistry Vol.238 No.-
<P>The new compounds NaCoCr2(PO4)(3), NaNiCr2(PO4)(3), and Na2Ni2Cr(PO4)(3) were synthesized by sol-gel method and their crystal structures were determined by using neutron powder diffraction data. These compounds were characterized by galvanometric cycling and cyclic voltammetry. NaCoCr2(PO4)(3), NaNiCr2(PO4)(3), and Na2Ni2Cr(PO4)(3) crystallize with a stuffed alpha-CrPO4-type structure. The structure consists of a 3D-framework made of octahedra and tetrahedra that are sharing corners and/or edges generating channels along [100] and [010], in which the sodium atoms are located. Of significance, in the structures of NaNiCr2(PO4)(3), and Na2Ni2Cr(PO4)(3) a statistical disorder Ni2+/Cr3+ was observed on both the 8g and 4a atomic positions, whereas in NaCoCr2(PO4)(3) the statistical disorder Co2+/Cr3+ was only observed on the 8g atomic position. When tested as negative electrode materials, NaCoCr2(PO4)(3), NaNiCr2(PO4)(3), and Na2Ni2Cr(PO4)(3) delivered specific capacities of 352, 385, and 368 mA h g(-1), respectively, which attests to the electrochemical activity of sodium in these compounds. (C) 2016 Elsevier Inc. All rights reserved.</P>
Magnetic transitions in the chiral armchair-kagome system Mn2Sb2O7
Peets, Darren C.,Sim, Hasung,Choi, Seongil,Avdeev, Maxim,Lee, Seongsu,Kim, Su Jae,Kang, Hoju,Ahn, Docheon,Park, Je-Geun American Physical Society 2017 Physical Review B Vol.95 No.1
<P>The competition between interactions in frustrated magnets allows a wide variety of new ground states, often exhibiting emergent physics and unique excitations. Expanding the suite of lattices available for study enhances our chances of finding exotic physics. Mn2Sb2O7 forms in a chiral, kagome-based structure in which a fourth member is added to the kagome-plane triangles to form an armchair unit and link adjacent kagome planes. This structural motif may be viewed as intermediate between the triangles of the kagome network and the tetrahedra in the pyrochlore lattice. Mn2Sb2O7 exhibits two distinct magnetic phase transitions, at 11.1 and 14.2 K, at least one of which has a weak ferromagnetic component. The magnetic propagation vector does not change through the lower transition, suggesting a metamagnetic transition or a transition involving a multicomponent order parameter. Although previously reported in the P3(1)21 space group, Mn2Sb2O7 actually crystallizes in P2, which allows ferroelectricity, and we show clear evidence of magnetoelectric coupling indicative of multiferroic order. The quasi-two-dimensional 'armchair-kagome' lattice presents a promising platform for probing chiral magnetism and the effect of dimensionality in highly frustrated systems.</P>
The Influence of Carbon Fiber Heat Treatment Temperature on Carbon-Carbon Brakes Characteristics
Andrey Galiguzov,Artem Malakho,Valery Kulakov,Anatoly Kenigfest,Evgeny Kramarenko,Viktor Avdeev 한국탄소학회 2013 Carbon Letters Vol.14 No.1
The effects of heat treatment temperature (HTT) of polyacrylonitrile-based carbon f-ber (CF) on the mechanical, thermal, and tribological properties of C/C composites were investigated. It was found that HTT (graphitization) of CF affects the thermal conductivity and mechanical and tribological characteristics of C/C composites. Thermal treatment of fibersat temperatures up to 2800°C led to a decrease of the wear rate and the friction coefficientof C/C composite-based discs from 7.0 to 1.1 μm/stop and from 0.356 to 0.269, respectively. The friction surface morphology and friction mechanism strongly depended on the mechanical properties of the CFs. The relief of the friction surface of composites based on CFs with finalgraphitization was also modified,compared to that of composites based on initial fibers.This phenomenon could be explained by modificationof the abrasive wear resistance of reinforcement fibersand consequently modificationof the friction and wearing properties of composites. Correlation of the graphitization temperature with the increased flexuraland compressive strength, apparent density, and thermal conductivity of the composites was also demonstrated.
Properties of spin-12triangular-lattice antiferromagnetsCuY2Ge2O8andCuLa2Ge2O8
Cho, Hwanbeom,Kratochví,lová,, Marie,Sim, Hasung,Choi, Ki-Young,Kim, Choong Hyun,Paulsen, Carley,Avdeev, Maxim,Peets, Darren C.,Jo, Younghun,Lee, Sanghyun,Noda, Yukio,Lawler, Michael J.,Pa American Physical Society 2017 Physical review. B Vol.95 No.14
<P>We found new two-dimensional (2D) quantum (S = 1/2) antiferromagnetic systems: CuRE2Ge2O8 (RE = Y and La). According to our analysis of high-resolution x-ray and neutron diffraction experiments, the Cu network of CuRE2Ge2O8 (RE = Y and La) exhibits a 2D triangular lattice linked via weak bonds along the perpendicular b axis. Our bulk characterizations from 0.08 to 400 K show that they undergo a long-range order at 0.51(1) and 1.09(4) K for the Y and La systems, respectively. Interestingly, they also exhibit field induced phase transitions. For theoretical understanding, we carried out the density functional theory (DFT) band calculations to find that they are typical charge-transfer-type insulators with a gap of E-g congruent to 2 eV. Taken together, our observations make CuRE2Ge2O8 (RE = Y and La) additional examples of low-dimensional quantum spin triangular antiferromagnets with the low-temperature magnetic ordering.</P>