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  2. Koichi Kusakabe

Koichi Kusakabe

  (草部 浩一)

Profile Information

Affiliation
Professor, Graduate School of Science Department of Material Science, University of Hyogo
Associate Professor, Graduate School of Engineering Science Department of Materials Engineering Science, Osaka University
Degree
Ph D in Science(The University of Tokyo)
Master of Science(The University of Tokyo)
J-GLOBAL ID
200901089608768091
researchmap Member ID
1000185126

Research Interests

 4

Research Areas

 3

Research History

 5

Awards

 1

Papers

 173
  • Keiki Fukumoto, Seunghee Lee, Shin-ichi Adachi, Yuta Suzuki, Koichi Kusakabe, Rikuto Yamamoto, Motoharu Kitatani, Kunio Ishida, Yoshinori Nakagawa, Michael Merkel, Daisuke Shiga, Hiroshi Kumigashira
    Scientific Reports, 14(1), May 8, 2024  
    Abstract Topological insulators (TI) hold significant potential for various electronic and optoelectronic devices that rely on the Dirac surface state (DSS), including spintronic and thermoelectric devices, as well as terahertz detectors. The behavior of electrons within the DSS plays a pivotal role in the performance of such devices. It is expected that DSS appear on a surface of three dimensional(3D) TI by mechanical exfoliation. However, it is not always the case that the surface terminating atomic configuration and corresponding band structures are homogeneous. In order to investigate the impact of surface terminating atomic configurations on electron dynamics, we meticulously examined the electron dynamics at the exfoliated surface of a crystalline 3D TI (Bi$$_2$$Se$$_3$$) with time, space, and energy resolutions. Based on our comprehensive band structure calculations, we found that on one of the Se-terminated surfaces, DSS is located within the bulk band gap, with no other surface states manifesting within this region. On this particular surface, photoexcited electrons within the conduction band effectively relax towards DSS and tend to linger at the Dirac point for extended periods of time. It is worth emphasizing that these distinct characteristics of DSS are exclusively observed on this particular surface.
  • 草部浩一
    まぐね/Magnetics Jpn., 19(2) 80-88, Apr, 2024  Peer-reviewedLead author
  • Yasuhiro Oishi, Motoharu Kitatani, Koichi Kusakabe
    Beilstein Journal of Organic Chemistry, 20 570-577, Mar 11, 2024  
    We theoretically analyze possible multiple conformations of protein molecules immobilized by 1-pyrenebutanoic acid succinimidyl ester (PASE) linkers on graphene. The activation barrier between two bi-stable conformations exhibited by PASE is confirmed to be based on the steric hindrance effect between a hydrogen on the pyrene group and a hydrogen on the alkyl group of this molecule. Even after the protein is supplemented, this steric hindrance effect remains if the local structure of the linker consisting of an alkyl group and a pyrene group is maintained. Therefore, it is likely that the kinetic behavior of a protein immobilized with a single PASE linker exhibits an activation barrier-type energy surface between the bi-stable conformations on graphene. We discuss the expected protein sensors when this type of energy surface appears and provide a guideline for improving the sensitivity, especially as an oscillator-type biosensor.
  • Halimah Harfah, Yusuf Wicaksono, Gagus Ketut Sunnardianto, Muhammad Aziz Majidi, Koichi Kusakabe
    Physical Chemistry Chemical Physics, 26(12) 9733-9740, Mar 6, 2024  
    Enhanced spin control in graphene/hBN MTJ: boron vacancy tuning yields high TMR ratio of 400%, paving the way for ultra-thin spin valves.
  • 草部浩一
    まぐね/Magnetics Jpn., 18(6) 287-294, Dec, 2023  Peer-reviewedLead author
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Misc.

 259
  • Ueda H, Nakano H, Kusakabe K
    Meeting abstracts of the Physical Society of Japan, 64(1), Mar, 2009  
  • Kusakabe Koichi, Nakanishi Akitaka
    Journal of the Physical Society of Japan, 78, 12, 124712(12) 124712-124712, 2009  
    To investigate the material dependence of the electronic structure of arsenide superconductors, the chemical trend of the Kohn–Sham band structures of a series of compounds, i.e., NaFeAs, NaCoAs, and NaNiAs, is studied by first-principles calculation based on generalized gradient approximation. Hypothetical structures of NaCoAs and NaNiAs in P4⁄nmm are found to be stable by structural optimization simulation. Results on the electronic states suggest that a characteristic two-dimensional electronic structure appearing as rodlike Fermi pockets is clearly found only in NaFeAs, while three-dimensional electronic structures are found in NaCoAs and NaNiAs with larger density of states than NaFeAs at the Fermi level, when paramagnetic electronic states are assumed.
  • Akitaka Nakanishi, Takahiro Ishikawa, Hitose Nagara, Kouichi Kusakabe
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 77(10), Oct, 2008  
    By means of first-principles calculations, we studied stable lattice structures and estimated superconducting transition temperature of CaSi2 at high pressure. Our simulation shows stability of the AlB2 structure in a pressure range above 17 GPa. In this structure, doubly degenerated optical phonon modes, in which the neighboring silicon atoms oscillate alternately in a silicon plane, show prominently strong interaction with the conduction electrons. In addition there exists a softened optical mode (out-of-plan motion of silicon atoms), whose strength of the electron-phonon interaction is nearly the same as the above mode. The density of states at the Fermi level in the AlB2 structure is higher than that in the trigonal structure. These findings and the estimation of the transition temperature strongly suggest that higher T-c is expected in the AlB2 structure than the trigonal structures which are known so far.
  • Hidetoshi Kizaki, Koichi Kusakabe, Soichiro Nogami, Hiroshi Katayama-Yoshida
    APPLIED PHYSICS EXPRESS, 1(10), Oct, 2008  
    A new mechanism of nano-catalyst generation based on the spinodal nano-decomposition in self-regenerating perovskite catalysts for automotive-emissions control is proposed. To demonstrate existence of the spinodal nano-decomposition in real perovskite catalysts, we performed first-principles calculations to evaluate the free energy of La(Fe(1-x)Pd(x))O(3) and La(Fe(1-x)Rh(x))O(3). The result indicates appearance of a spinodal region in the phase diagram of each material. Formation of nano-catalyst particles in the perovskite host matrix is crucial for the self-regeneration of perovskite catalyst. Based on the spinodal nano-decomposition model, possible materials are designed for new three-way catalyst with no contents of precious metal. (c) 2008 The Japan Society of Applied Physics
  • Hidetoshi Kizaki, Koichi Kusakabe, Soichiro Nogami, Hiroshi Katayama-Yoshida
    APPLIED PHYSICS EXPRESS, 1(10), Oct, 2008  
    A new mechanism of nano-catalyst generation based on the spinodal nano-decomposition in self-regenerating perovskite catalysts for automotive-emissions control is proposed. To demonstrate existence of the spinodal nano-decomposition in real perovskite catalysts, we performed first-principles calculations to evaluate the free energy of La(Fe(1-x)Pd(x))O(3) and La(Fe(1-x)Rh(x))O(3). The result indicates appearance of a spinodal region in the phase diagram of each material. Formation of nano-catalyst particles in the perovskite host matrix is crucial for the self-regeneration of perovskite catalyst. Based on the spinodal nano-decomposition model, possible materials are designed for new three-way catalyst with no contents of precious metal. (c) 2008 The Japan Society of Applied Physics
  • Akitaka Nakanishi, Takahiro Ishikawa, Hitose Nagara, Kouichi Kusakabe
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 77(10), Oct, 2008  
    By means of first-principles calculations, we studied stable lattice structures and estimated superconducting transition temperature of CaSi2 at high pressure. Our simulation shows stability of the AlB2 structure in a pressure range above 17 GPa. In this structure, doubly degenerated optical phonon modes, in which the neighboring silicon atoms oscillate alternately in a silicon plane, show prominently strong interaction with the conduction electrons. In addition there exists a softened optical mode (out-of-plan motion of silicon atoms), whose strength of the electron-phonon interaction is nearly the same as the above mode. The density of states at the Fermi level in the AlB2 structure is higher than that in the trigonal structure. These findings and the estimation of the transition temperature strongly suggest that higher T-c is expected in the AlB2 structure than the trigonal structures which are known so far.
  • Seike A., Sogo S., Kusakabe K.
    Meeting abstracts of the Physical Society of Japan, 63(2) 203-203, Aug 25, 2008  
  • Ona S, Murakami M, Nakamoto Y, Kagayama T, Shimizu K, Kusakabe K, Furusho H, Taguchi E, Watanuki T, Ohishi Y
    Meeting Abstracts of the Physical Society of Japan, 63(2), Aug 25, 2008  
  • Ueda H, Nakano H, Kusakabe K
    Meeting abstracts of the Physical Society of Japan, 63(2), Aug, 2008  
  • Hiroshi Katayama-Yoshida, Koichi Kusakabe, Hidetoshi Kizaki, Akitaka Nakanishi
    APPLIED PHYSICS EXPRESS, 1(8), Aug, 2008  
    Based on the microscopic mechanisms of (1) charge-excitation-induced negative effective U in s(1) or d(9) electronic configurations, and (2) exchange-correlation-induced negative effective U in d(4) or d(6) electronic configurations, we propose a general rule and materials design of negative effective U system in itinerant (ionic and metallic) system for the realization of high-T-c superconductors. We design a T-c-enhancing layer (or clusters) of charge-excitation-induced negative effective U connecting the superconducting layers for the realistic systems. (C) 2008 The Japan Society of Applied Physics.
  • Hiroshi Katayama-Yoshida, Koichi Kusakabe, Hidetoshi Kizaki, Akitaka Nakanishi
    APPLIED PHYSICS EXPRESS, 1(8), Aug, 2008  
    Based on the microscopic mechanisms of (1) charge-excitation-induced negative effective U in s(1) or d(9) electronic configurations, and (2) exchange-correlation-induced negative effective U in d(4) or d(6) electronic configurations, we propose a general rule and materials design of negative effective U system in itinerant (ionic and metallic) system for the realization of high-T-c superconductors. We design a T-c-enhancing layer (or clusters) of charge-excitation-induced negative effective U connecting the superconducting layers for the realistic systems. (C) 2008 The Japan Society of Applied Physics.
  • Takahiro Ishikawa, Ayako Ichikawa, Hitose Nagara, Masaaki Geshi, Koichi Kusakabe, Naoshi Suzuki
    PHYSICAL REVIEW B, 78(2), Jul, 2008  
  • WAKABAYASHI Katsunori, KUSAKABE Koichi
    Butsuri, 63(5) 344-352, May 5, 2008  
    The discovery of fullerene molecules and carbon nanotubes has triggered intensive research on various nanocarbon systems. Recent progress of fine processing technology enables us to fabricate the graphene devices. In this article, we elucidate that the graphene edges and their shape crucially affect on physical properties of nano-graphene and graphene nanoribbons.
  • Yuichi Ikuno, Koichi Kusakabe
    e-Journal of Surface Science and Nanotechnology, 6 103-106, Apr 2, 2008  
    We have reinvestigated the method to determine the work function of metals by the first-principles electronic structure calculation using the plane-wave expansion method with pseudo-potentials. Changing width of a vacuum layer of a slab model, we obtained the Fermi level measured from the effective Kohn-Sham potential at the center of the vacuum layer. By extrapolating the values of the Fermi level to the infinite vacuum-layer limit, the Fermi energy is determined. We propose a fitting function for the extrapolation. This function works well for determination of the highest occupied level and the lowest unoccupied level of materials with a surface relative to the vacuum level in the Kohn-Sham scheme. The obtained work functions for [100], [110] and [111] surfaces of three noble metals, Rh, Pd and Pt are comparable to the known theoretical estimation as well as the experimental values. © 2008 The Surface Science Society of Japan.
  • Ishikawa T., Nagara H., Kusakabe K., Suzuki N.
    Meeting abstracts of the Physical Society of Japan, 63(1) 763-763, Feb 29, 2008  
  • Nakanishi A., Kusakabe K.
    Meeting abstracts of the Physical Society of Japan, 63(1) 763-763, Feb 29, 2008  
  • Ono Youky, Kusakabe Koichi, Nakayama Takashi
    Meeting abstracts of the Physical Society of Japan, 63(1) 271-271, Feb 29, 2008  
  • Ueda H, Nakano H, Kusakabe K
    Meeting abstracts of the Physical Society of Japan, 63(1), Feb, 2008  
  • F. Kanetake, A. Harada, T. Rachi, H. Nagara, H. Mukuda, K. Kusakabe, Y. Kitaoka, N. Suzuki, K. Tanigaki, K. Itoh, E. E. Haller
    JOINT 21ST AIRAPT AND 45TH EHPRG INTERNATIONAL CONFERENCE ON HIGH PRESSURE SCIENCE AND TECHNOLOGY, 121, 2008  
    Through Ge-73-NMR measurements and ab initio calculations, we have studied electronic properties of a type-III clathrate compound Ba24Ge100. At ambient pressure, the nuclear spin-lattice relaxation rate 1/T1T has a peak around 200K followed by an activation type decrease with decreasing temperature and it becomes constant at very low temperatures. Near the peak temperature, the successive structural transformations have been observed at T-S1 = 215K and T-S2 = 180 K. The constant value of 1/T1T at low temperatures is considerably smaller than the value at temperatures higher than T-S1, which implies that the density of states at the Fermi level D(E-F) significantly decreases from the high temperature value at ambient pressure. From ab initio calculations on Ba24Ge100 as well as Ba24Si100, we speculate the phase changes of Ba24Ge100 in the relevant region of the T-P plane. Our results of NMR measurements and D(E-F) calculations for the P4(1)32 and an R3 structures imply that, at high pressures similar to 2.8GPa, there should be increase of D(E-F) from the value at ambient pressure and low temperatures. We conclude that this result is predominantly related with the large enhancement of the superconducting transition temperature T-c from 0.24K (at P = 0) to 3.8K (at P = 2.7GPa) observed in Ba24Ge100.
  • Hitose Nagara, Takahiro Ishikawa, Koichi Kusakabe, Naoshi Suzuki
    ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 64 C223-C223, 2008  
  • Takahiro Ishikawa, Ayako Ichikawa, Hitose Nagara, Masaaki Geshi, Koichi Kusakabe, Naoshi Suzuki
    PHYSICAL REVIEW B, 77(2), Jan, 2008  
    We searched for the structure of calcium in phases IV and V by a metadynamics simulation based on ab initio calculations, and found two structures. One is a tetragonal lattice which consists of two helical chains along the c axis. The other is an orthorhombic lattice of four zigzag chains. We have calculated the x-ray diffraction patterns and enthalpies of the two structures discovered by our simulation. From comparisons of the patterns with the experimental x-ray patterns of the phases IV and V and from the pressure dependence of the enthalpies, we conclude that the structure with a helical pattern corresponds to phase IV and the structure with a zigzag pattern to phase V.
  • .e-J. Surf. Sci. Nanotech., 6, 103-106, 2008  
  • Takahiro Ishikawa, Ayako Ichikawa, Hitose Nagara, Masaaki Geshi, Koichi Kusakabe, Naoshi Suzuki
    PHYSICAL REVIEW B, 77(2), Jan, 2008  
    We searched for the structure of calcium in phases IV and V by a metadynamics simulation based on ab initio calculations, and found two structures. One is a tetragonal lattice which consists of two helical chains along the c axis. The other is an orthorhombic lattice of four zigzag chains. We have calculated the x-ray diffraction patterns and enthalpies of the two structures discovered by our simulation. From comparisons of the patterns with the experimental x-ray patterns of the phases IV and V and from the pressure dependence of the enthalpies, we conclude that the structure with a helical pattern corresponds to phase IV and the structure with a zigzag pattern to phase V.
  • Ishikawa T., Ichikawa A., Nagara H., Kusakabe K., Suzuki N.
    Meeting abstracts of the Physical Society of Japan, 62(2) 901-901, Aug 21, 2007  
  • Nakanishi A., Ishikawa T., Nagara H., Kusakabe K.
    Meeting abstracts of the Physical Society of Japan, 62(2) 647-647, Aug 21, 2007  
  • Nakano H, Ueda H, Tonooka S, Kusakabe K, Suzuki N
    Meeting abstracts of the Physical Society of Japan, 62(2), Aug, 2007  
  • Ishikawa Takahiro, Nagara Hitose, Kusakabe Koichi, Suzuki Naoshi
    Meeting abstracts of the Physical Society of Japan, 62(1) 808-808, Feb 28, 2007  
  • 小林陽介, 福井賢一, 草部浩一, 榎敏明
    炭素, (228) 166-173, 2007  
  • Yousuke Kobayashi, Koichi Kusakabe, Ken-ichi Fukui, Toshiaki Enoki
    PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 34(1-2) 678-681, Aug, 2006  
    The structure-dependent edge state of graphite is investigated by ultra-high-vacuum scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) observations. On a hydrogenated zigzag edge, bright spots assigned to edge states are observed together with a (root 3 x root 3) R30 degrees superlattice. The STS measurement shows that the bright spots originate from a peak near the Fermi level at V-S = -30mV. In contrast, on a hydrogenated armchair edge, such bright spots are not observed. Even in the hydrogenated armchair edge, however, edge states are observed at defect points, where zigzag edges are partially created. The distribution of the edge states is dependent on the detailed structure of the defect. (c) 2006 Elsevier B.V. All rights reserved.
  • Yousuke Kobayashi, Koichi Kusakabe, Ken-ichi Fukui, Toshiaki Enoki
    PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 34(1-2) 678-681, Aug, 2006  
    The structure-dependent edge state of graphite is investigated by ultra-high-vacuum scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) observations. On a hydrogenated zigzag edge, bright spots assigned to edge states are observed together with a (root 3 x root 3) R30 degrees superlattice. The STS measurement shows that the bright spots originate from a peak near the Fermi level at V-S = -30mV. In contrast, on a hydrogenated armchair edge, such bright spots are not observed. Even in the hydrogenated armchair edge, however, edge states are observed at defect points, where zigzag edges are partially created. The distribution of the edge states is dependent on the detailed structure of the defect. (c) 2006 Elsevier B.V. All rights reserved.
  • K Kusakabe, M Takahashi, N Suzuki
    PHYSICA B-CONDENSED MATTER, 378-80 271-272, May, 2006  
    To perform the first-principles calculation of a non-uniform electron system with both localized and delocalized electrons, we have developed a calculational method based on a newly developed density-matrix functional theory. Our scheme is based on a recent rigorous result on uniqueness of an effective impurity Anderson model which reproduces a positive-definite density-density correlation as well as the single electron density. A tractable algorithm to determine the U term using estimation of an impurity problem by the transcorrelated method is proposed. (c) 2006 Elsevier B.V. All rights reserved.
  • K Kusakabe, M Takahashi, N Suzuki
    PHYSICA B-CONDENSED MATTER, 378-80 271-272, May, 2006  
    To perform the first-principles calculation of a non-uniform electron system with both localized and delocalized electrons, we have developed a calculational method based on a newly developed density-matrix functional theory. Our scheme is based on a recent rigorous result on uniqueness of an effective impurity Anderson model which reproduces a positive-definite density-density correlation as well as the single electron density. A tractable algorithm to determine the U term using estimation of an impurity problem by the transcorrelated method is proposed. (c) 2006 Elsevier B.V. All rights reserved.
  • Shusuke Yamanaka, Kazuto Nakata, Toshikazu Takada, Koichi Kusakabe, Jesus M. Ugalde, Kizashi Yamaguchi
    Chemistry Letters, 35(3) 242-247, Mar 5, 2006  
    We review a recently developed ab initio multireference (MR)-density functional theory (DFT) approach based on the partially interacting reference systems. Instead of Kohn-Sham equations, we introduce the auxiliary CI equation with the effective DFT potential field. For practice, we classify electrons of the target system into valence electrons and other electrons. The former plays the quantum resonating feature of electronic structure of molecular species, while the latter affects the electronic properties via the effective correlation potential for the former electrons. The theoretical devices in our MR-DFT are introduced to avoid the double counting problem for any combination of a wavefunction and a correlation functional. Some numerical examples are presented. Copyright © 2006 The Chemical Society of Japan.
  • Kobayashi Y., Kusakabe K., Fukui K., Enoki T.
    Meeting abstracts of the Physical Society of Japan, 61(1) 856-856, Mar 4, 2006  
  • Kusakabe Koichi, Kobayashi Yosuke, Fukui Ken-ichi, Enoki Toshiaki
    Meeting abstracts of the Physical Society of Japan, 61(1) 857-857, Mar 4, 2006  
  • Uodome A, Kagayama T, Nakamoto Y, Shimizu K, Kusakabe K, Nishikawa Y, Murakami M, Ohishi Y, Watanuki T
    Meeting Abstracts of the Physical Society of Japan, 61(1), Mar 4, 2006  
  • Y Kobayashi, K Fukui, T Enoki, K Kusakabe
    PHYSICAL REVIEW B, 73(12), Mar, 2006  
    The edge states that emerge at hydrogen-terminated zigzag edges embedded in dominant armchair edges of graphite are carefully investigated by ultrahigh-vacuum scanning tunneling microscopy (STM) measurements. The edge states at the zigzag edges have different spatial distributions dependent on the alpha- or beta-site edge carbon atoms. In the case that the defects consist of a short zigzag (or a short Klein) edge, the edge state is present also near the defects. The amplitude of the edge state distributing around the defects in an armchair edge often has a prominent hump in a direction determined by detailed local atomic structure of the edge. The tight binding calculation based on the atomic arrangements observed by STM reproduces the observed spatial distributions of the local density of states.
  • Phys. Rev. B, 73, 125415-1-8, 2006  
  • Ishikawa Takahiro, Nagara Hitose, Kusakabe Koichi, Suzuki Naoshi
    Meeting abstracts of the Physical Society of Japan, 60(2) 679-679, Aug 19, 2005  
  • UODOME A, NAKAMOTO Y, KAGAYAMA T, SHIMIZU K, KUSAKABE K, NISHIKAWA Y, MURAKAMI M, OHISHI Y, WATANUKI T
    Meeting Abstracts of the Physical Society of Japan, 60(2), Aug 19, 2005  
  • Y Kobayashi, K Fukui, T Enoki, K Kusakabe, Y Kaburagi
    PHYSICAL REVIEW B, 71(19), May, 2005  
    The presence of structure-dependent edge states of graphite is revealed by both ambient and ultrahigh-vacuum (UHV) scanning tunneling microscopy and scanning tunneling spectroscopy observations. On a hydrogenated zigzag (armchair) edge, bright spots are (are not) observed together with a (root 3 X root 3)R30 degrees super-lattice near the Fermi level (Vs similar to-30 mV for a peak of the local density of states) under UHV. demonstrating that a zigzag edge is responsible for the edge states, although there is no appreciable difference between as-prepared zigzag and armchair edges in air. Even in the hydrogenated armchair edge, however, bright spots are observed at defect points, at which partial zigzag edges are created in the armchair edge.
  • Y Kobayashi, K Fukui, T Enoki, K Kusakabe, Y Kaburagi
    PHYSICAL REVIEW B, 71(19), May, 2005  
    The presence of structure-dependent edge states of graphite is revealed by both ambient and ultrahigh-vacuum (UHV) scanning tunneling microscopy and scanning tunneling spectroscopy observations. On a hydrogenated zigzag (armchair) edge, bright spots are (are not) observed together with a (root 3 X root 3)R30 degrees super-lattice near the Fermi level (Vs similar to-30 mV for a peak of the local density of states) under UHV. demonstrating that a zigzag edge is responsible for the edge states, although there is no appreciable difference between as-prepared zigzag and armchair edges in air. Even in the hydrogenated armchair edge, however, bright spots are observed at defect points, at which partial zigzag edges are created in the armchair edge.
  • Ishikawa T., Nagara H., Kusakabe K., Suzuki N.
    Meeting abstracts of the Physical Society of Japan, 60(1) 735-735, Mar 4, 2005  
  • Kobayashi Y., Fukui K., Enoki T., Kusakabe K.
    Meeting abstracts of the Physical Society of Japan, 60(1) 798-798, Mar 4, 2005  
  • Ogasahara A, Kusakabe K
    Meeting abstracts of the Physical Society of Japan, 59(2) 503-503, Aug 25, 2004  
  • S Tonooka, H Nakano, K Kusakabe, N Suzuki
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 73(6) 1597-1601, Jun, 2004  
    Magnetic interactions in the nanoscale ferrimagnetic ring [Mn(hfac)(2)NITPh](6) abbreviated as Mn6R6 are estimated by comparing experimental data with our numerical data as obtained from the exact diagonalization of a Heisenberg model. Our results suggest that next nearest neighbor radical-radical interactions are essential to reproduce the magnetic structure of Mn6R6 well. The existence of these interactions means that Mn6R6 is a kind of frustrated spin cluster. We predict that the field derivative of magnetization should have two peaks in the range of magnetic field 380-420 T, which is beyond the range of current experimental observations. We also find that the local spin density of the frustrated model shows a different behavior from those of non-frustrated models studied in preceding works.
  • S Tonooka, H Nakano, K Kusakabe, N Suzuki
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 73(6) 1597-1601, Jun, 2004  
    Magnetic interactions in the nanoscale ferrimagnetic ring [Mn(hfac)(2)NITPh](6) abbreviated as Mn6R6 are estimated by comparing experimental data with our numerical data as obtained from the exact diagonalization of a Heisenberg model. Our results suggest that next nearest neighbor radical-radical interactions are essential to reproduce the magnetic structure of Mn6R6 well. The existence of these interactions means that Mn6R6 is a kind of frustrated spin cluster. We predict that the field derivative of magnetization should have two peaks in the range of magnetic field 380-420 T, which is beyond the range of current experimental observations. We also find that the local spin density of the frustrated model shows a different behavior from those of non-frustrated models studied in preceding works.
  • S Tonooka, H Nakano, K Kusakabe, N Suzuki
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 73(6) 1597-1601, Jun, 2004  
    Magnetic interactions in the nanoscale ferrimagnetic ring [Mn(hfac)(2)NITPh](6) abbreviated as Mn6R6 are estimated by comparing experimental data with our numerical data as obtained from the exact diagonalization of a Heisenberg model. Our results suggest that next nearest neighbor radical-radical interactions are essential to reproduce the magnetic structure of Mn6R6 well. The existence of these interactions means that Mn6R6 is a kind of frustrated spin cluster. We predict that the field derivative of magnetization should have two peaks in the range of magnetic field 380-420 T, which is beyond the range of current experimental observations. We also find that the local spin density of the frustrated model shows a different behavior from those of non-frustrated models studied in preceding works.
  • A Ogasahara, K Kusakabe
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 73(6) 1426-1429, Jun, 2004  
    Electron transport is investigated theoretically for an electron which is coupled to a localized spin system. The dc electrical conductivity of spin-fermion models in one dimension is studied by the direct numerical estimation of the Kubo formula. The dependence of the conductivity on temperature and external magnetic field is investigated. When the localized spins are antiferromagnetically coupled on a chain, the conductivity shows a monotonic increase with magnetic field, which is ordinary magnetoresistance. However, in a system where the localized spins form an antiferromagnetically coupled two-leg ladder, the conductivity shows an anomalous non-monotonic field dependence. Analysis of the spin configuration of the localized spin system reveals that quantum fluctuation determines the conductivity through a dimerized-rung spin configuration, and the formation of local triplets on the ladder rungs causes the decrease in conductivity.
  • S Tonooka, H Nakano, K Kusakabe, N Suzuki
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 73(6) 1597-1601, Jun, 2004  
    Magnetic interactions in the nanoscale ferrimagnetic ring [Mn(hfac)(2)NITPh](6) abbreviated as Mn6R6 are estimated by comparing experimental data with our numerical data as obtained from the exact diagonalization of a Heisenberg model. Our results suggest that next nearest neighbor radical-radical interactions are essential to reproduce the magnetic structure of Mn6R6 well. The existence of these interactions means that Mn6R6 is a kind of frustrated spin cluster. We predict that the field derivative of magnetization should have two peaks in the range of magnetic field 380-420 T, which is beyond the range of current experimental observations. We also find that the local spin density of the frustrated model shows a different behavior from those of non-frustrated models studied in preceding works.

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