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  2. 山田 豊和

山田 豊和

ヤマダ トヨカズ  (Toyo Kazu Yamada)

基本情報

所属
千葉大学 大学院工学研究院 准教授
J-GLOBAL ID
200901093690188321
researchmap会員ID
5000019552
外部リンク
I, Toyo Kazu Yamada, started my research from 1998. When I was a Master student (1998-2000) I developed a Mott detector for visualizing surface magnetic domains by combining with SEM (scanning electron microscopy), which is so-called spin-polarized SEM (or SEMPA). During that time, Prof. Dr. Tadashi Mizoguchi and Dr. Jun Fujii were my supervisors (Gakushuin University, Tokyo). From 2000 till 2004, I was a PhD student of Radboud University Nijmegen (Prof. Dr. Herman van Kempen, The Netherlands) and Gakushuin University (Prof. Dr. Tadashi Mizoguchi, Japan): double degree program. I developed spin-polarized STM (scanning tunneling microscopy). Atomic-size magnetic domain structures of ultra thin layerwise antiferromagnetically coupled Mn films on Fe(001) were deeply studied at 300 K in UHV. During 2004-2008, after I got two PhD degrees, I got a JSPS research fellow (PD) position, and subsequently got an Assistant Professor position at Gakushuin University, where X-ray, AFM, VSM, Kerr, and many experimental setup treatments for education were learned. After the hard time due to too much education matter, I decided to go to Germany to join exciting researches. I was studying with Prof. Dr. Wulf Wulfhekel at Karlsruhe Institute of Technology (KIT) in 2008-2010 as a Humboldt research fellow. I have studied organic molecules by using spin-polarized STM and found that single phthalocyanine molecules can be the smallest magneto resistance sensor. Also, magneto electric coupling (bcc-fcc phase switching by electric field) was found on the surface of Fe nano islands on Cu(111). Further, high and low spin state in the spin crossover molecules was tuned by injecting electrons from the STM tip. In 2010, I got a Tenure-Track Associate Professor position at Chiba Univ. in Japan, and in 2015, I got the Tenure. Starting from 2010, in Chiba Univ., I opened my lab. So far (-2018), four home-built UHV-STM setups (three low temperatures and one room temperature) have been developed. Using these setups combined with spin-polarized STM techniques, now, we are studying single magnetic atoms, organic molecules, graphene nanoribbons, Fe/MgO interface, nano magnets on s-wave superconductor, and life molecules.

研究キーワード

 32

研究分野

 13

経歴

 15
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学歴

 8
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委員歴

 27
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受賞

 12
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論文

 85
  • Stefan Schmaus, Alexei Bagrets, Yasmine Nahas, Toyo K. Yamada, Annika Bork, Martin Bowen, Eric Beaurepaire, Ferdinand Evers, Wulf Wulfhekel
    NATURE NANOTECHNOLOGY 6(3) 185-189 2011年3月  査読有り
    Magnetoresistance is a change in the resistance of a material system caused by an applied magnetic field. Giant magnetoresistance occurs in structures containing ferromagnetic contacts separated by a metallic non-magnetic spacer, and is now the basis of read heads for hard drives and for new forms of random access memory. Using an insulator (for example, a molecular thin film) rather than a metal as the spacer gives rise to tunnelling magnetoresistance, which typically produces a larger change in resistance for a given magnetic field strength, but also yields higher resistances, which are a disadvantage for real device operation. Here, we demonstrate giant magnetoresistance across a single, nonmagnetic hydrogen phthalocyanine molecule contacted by the ferromagnetic tip of a scanning tunnelling microscope. We measure the magnetoresistance to be 60% and the conductance to be 0.26G(o), where G(o) is the quantum of conductance. Theoretical analysis identifies spin-dependent hybridization of molecular and electrode orbitals as the cause of the large magnetoresistance.
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  • 山田豊和
    日本磁気学会誌まぐね (6) 333-341 2011年  査読有り
  • 山田豊和
    表面科学 32(6) 361-367 2011年  査読有り招待有り筆頭著者責任著者
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  • L. Gerhard, T. K. Yamada, T. Balashov, A. F. Takacs, R. J. H. Wesselink, M. Daene, M. Fechner, S. Ostanin, A. Ernst&apos, I. Mertig, W. Wulfhekel
    NATURE NANOTECHNOLOGY 5(11) 792-797 2010年11月  査読有り
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  • Irisawa, T., Yamada, T.K., Mizoguchi, T.
    New Journal of Physics 11(11) 113031-113031 2009年11月17日  筆頭著者
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  • Yamada, T.K., Tamura, H., Shishido, M., Irisawa, T., Mizoguchi, T.
    Surface Science 603(2) 315-319 2009年1月  査読有り筆頭著者
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  • Gaku Aoki, Toyo K. Yamada, Mayu Arii, Shuichi Kojima, Tadashi Mizoguchi
    Journal of Biochemistry 144(1) 15-19 2008年7月  査読有り
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  • T. Irisawa, T.K. Yamada, T. Mizoguchi
    6th International Symposium on Atomic Level Characterizations for New Materials and Devices 2007(ALC07(Kanazawa)) Proceedings 2008年  
  • Yamada, T.K., Mart{\'i}nez, E., Vega, A., Robles, R., Stoeffler, D., V{\'a}zquez De Parga, A.L., Mizoguchi, T., Van Kempen, H.
    Nanotechnology 18(23) 235702-235702 2007年6月13日  査読有り筆頭著者
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  • T.K. Yamada, T.Mizoguchi
    The Physical Society of Japan "BUTSURI" 62(7) 499-508 2007年6月  査読有り招待有り筆頭著者
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  • T. K. Yamada
    Report of The Magnetics Society of Japan Symposium (155) 41-46 2007年  査読有り
  • T.K. Yamada, T. Mizoguchi
    固体物理 Solid State Physics 42(11) 749-756 2007年  査読有り招待有り筆頭著者
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  • Yamada, T.K., V{\'a}zquez De Parga, A.L., Bischoff, M.M.J., Mizoguchi, T., Van Kempen, H.
    Surface Science 600(5) 1048-1053 2006年3月  査読有り筆頭著者
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  • Matsuda, T., Tonomura, A., Yamada, T.K., Okuyama, D., Mizuno, N., De Parga, A.L.V.V., Van Kempen, H., Mizoguchi, T.
    IEEE Transactions on Magnetics 41(10) 3727-3729 2005年10月  責任著者
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  • T. K. Yamada, R. Robles, E. Martinez, M. M. J. Bischoff, A. Vega, A. L. Vázquez de Parga, T. Mizoguchi, H. van Kempen
    Physical Review B 72(1) 2005年7月5日  査読有り筆頭著者
    In this work we explore by means of spin-polarized scanning tunneling microcopy/spectroscopy (SP-STM/STS) and ab initio calculations the magnetic and electronic properties of thin MnAu alloyed films. The MnAu films are produced by deposition of small amounts of Au at RT on a Mn(001) surface. On the scanning tunneling microscopy images the surface of the AuMn alloy presents a c(2×2) reconstruction. From the SP-STM/STS measurements we find out that the MnAu alloy layers are coupled antiferromagnetically with the layers above and below. Comparing the result from the ab initio calculations with the spin-polarized measurements we found that the origin of the magnetic contrast is due to a spin-polarized peak at 0.15eV above the Fermi level spatially placed on the Mn sites. In the calculations we also found that the magnetic moments of the Mn atoms are higher in the alloy layers than in the pure Mn films. © 2005 The American Physical Society.
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  • Yamada, T.K., V{\'a}zquez De Parga, A.L., Bischoff, M.M.J., Mizoguchi, T., Van Kempen, H.
    Microscopy Research and Technique 66(2-3) 93-104 2005年2月  査読有り招待有り筆頭著者
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  • T.K. Yamada, T. Mizoguchi
    まてりあ : 日本金属学会会報 Materia Japan 44 975 2005年  
  • T. K. Yamada
    Radboud University Nijmegen 1-193 2005年  査読有り
  • T.K. Yamada, T. Mizoguchi
    The Surface Science Society of Japan 26(1) 2-10 2005年  
  • Yamada, T.K., Bischoff, M.M.J., V{\'a}zquez de Parga, A.L., Mizoguchi, T., Van Kempen, H.
    Surface Science 558(1-3) 201-210 2004年6月  査読有り筆頭著者
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  • T. K. Yamada
    Gakushuin University 1-113 2004年  査読有り
  • T. Mizoguchi, T.K. Yamada
    Journal of the Magnetics Society of Japan 28 1142-1149 2004年  
  • MMJ Bischoff, CM Fang, RA De Groot, GMM Heijnen, MI Katsnelson, OY Kolesnychenko, R De Kort, AI Lichtenstein, AJ Quinn, ALV de Parma, TK Yamada, H Van Kempen
    ACTA PHYSICA POLONICA A 104(3-4) 231-243 2003年9月  査読有り
    The surface states of 3d transition metals are studied by scanning tunneling microscopy and scanning tunneling spectroscopy. The results show that surface states can be used for chemical identification with high spatial resolution. The spin polarized nature of the surface states allows us to obtain magnetic contrast in scanning tunneling miroscopy imaging with near atomic resolution. For Cr(100) we found that the surface state close to the Fermi level can be explained by an orbital Kondo resonance surface state.
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  • MMJ Bischoff, TK Yamada, CM Fang, RA de Groot, H van Kempen
    PHYSICAL REVIEW B 68(4) 045422 2003年7月  査読有り
    Scanning tunneling spectroscopy is used to study the local electronic structure of Fe(001) whiskers. The influence of a voltage dependent background on the apparent peak energies in the dI/dV curves is discussed. A relation between this background and the apparent barrier height is established. The previously reported spin-polarized d(z)2-like surface state is shown to shift by an amount of 0.04 eV to higher energies at isolated oxygen impurities on the Fe(001) surface. The surface state disappears on both [100] and [110] directed steps. Finally, we investigated size effects by studying the behavior of the surface state on nanometer-sized Fe islands. Besides the surface-state quenching at the step edges, a peak shift to higher energies is observed for decreasing island sizes.
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  • TK Yamada, MMJ Bischoff, GMM Heijnen, T Mizoguchi, H Van Kempen
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 42(7B) 4688-4691 2003年7月  査読有り
    Normalized differential tunneling conductivities obtained with Fe-coated W tips show a spin-polarized peak around +0.8 V on ultrathin bet Mn films grown on Fe(001)-whiskers. This spin-polarized peak results in a clear magnetic contrast in spectroscopic images. Our normalization removes the influence of the tunneling probability and makes the spectroscopic curves most reliable for a derivation of the spin-resolved sample density of states (DOS) at positive voltages. From this analysis we conclude that the magnetic contrast in our spectroscopic maps is caused by a highly polarized DOS. Furthermore, a, tip polarization of about 15% is found.
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  • MMJ Bischoff, TK Yamada, H van Kempen
    PHYSICAL REVIEW B 67(16) 165403 2003年4月  査読有り
    Scanning tunneling microscopy measurements show that the growth of about half a monolayer Au on Fe(001) at a temperature of 170 degreesC leads after a postanneal at 700 degreesC to an island free and homogeneously alloyed surface layer. The surface alloying is in contrast to the bulk where Au and Fe are immiscible. Strong chemical contrast in the images allows us to analyze the short-range order of this surface alloy. Two independent methods are considered: the first method extracts pair occupation probabilities directly from digitized images, the second method makes use of the autocorrelation of filtered images. Both methods lead to the same conclusion: only for the nearest-neighbor sites a strong preference for unlike species is found; for further sites the probabilities follow a random distribution. Scanning tunneling spectroscopy measurements on the alloyed AuFe surface are used to corroborate the interpretation of the chemical contrast. Furthermore, the spectroscopy results show that the Fe(001) surface state shifts to higher energies on areas where pure Fe patches are confined by Au atoms.
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  • TK Yamada, MMJ Bischoff, T Mizoguchi, H van Kempen
    APPLIED PHYSICS LETTERS 82(9) 1437-1439 2003年3月  筆頭著者
    The present letter describes a method to make a spin-polarized scanning tunneling microscopy tip by applying voltage pulses between a W tip and a magnetic sample. This spin-polarized tip has the similar characteristics as an Fe-coated W tip, which was confirmed by observations of antiferromagnetically coupled ferromagnetic Mn(001) layers (>3 ML) grown on an Fe(001) whisker at 370 K. Furthermore, we demonstrate that these voltage pulses can vary the tip magnetization direction. (C) 2003 American Institute of Physics.
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  • TK Yamada, MMJ Bischoff, GMM Heijnen, T Mizoguchi, H van Kempen
    PHYSICAL REVIEW LETTERS 90(5) 056803 2003年2月  査読有り筆頭著者
    We report the observation of a magnetic contrast of up to 20% in the scanning tunneling spectroscopy dI/dV maps obtained with Fe-coated tips on Mn(001) layers grown on an Fe(001) whisker at 370 K. These nanometer resolution microscopy results show that the layers couple antiferromagnetically. By normalizing the dI/dV curves by tunneling probability functions, we found a spin-dependent peak on the body-centered-tetragonal (bct) Mn(001) surface at +0.8 V, whose high spin polarization gives rise to the dI/dV map contrast. Band structure calculations allow one to identify the +0.8 V peak as due to two spin-polarized d(z)(2) surface states.
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  • T.K. Yamada, A.L. Vazquez, de Parga, M.M.J. Bischoff, T. Mizoguchi, H. van Kempen
    AIP Conf. Proc. 696 608-614 2003年  筆頭著者
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  • TK Yamada, MMJ Bischoff, T Mizoguchi, H van Kempen
    SURFACE SCIENCE 516(1-2) 179-190 2002年9月  査読有り筆頭著者
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  • MMJ Bischoff, T Yamada, AJ Quinn, H van Kempen
    SURFACE SCIENCE 501(1-2) 155-167 2002年3月  査読有り
    The submonolayer growth of Mn on Fe(0 0 1) in the temperature range between 50 and 200 degreesC is studied by scanning tunneling microscopy and scanning tunneling spectroscopy. For growth temperatures above 100 degreesC, atomically resolved STM images with chemical contrast clearly reveal the incorporation of Mn atoms in the Fe(0 0 1) substrate. The fraction of place exchanged Mn atoms is observed to increase with growth temperature. Although on islands a c(2 x 2) structure forms locally which is attributed to an ordered MnFe surface alloy, long range order could not be obtained for the growth temperatures and coverages studied. Spectroscopy results are presented for clean Fe(0 0 1), pure Mn ad-islands, single incorporated Mn atoms and c(2 x 2)-ordered MnFe areas. In contrast to embedded Cr atoms in the Fe(0 0 1) surface [Phys. Rev. Lett. 76 (1996) 41751, isolated embedded Mn atoms do not lead to double peak structures in dI/dV curves. Nevertheless, on the ordered c(2 x 2) MnFe structure and the pure Mn monoatomic islands surface states are detected as peaks in the dI/dV and (dI/dV)/(I/V) curves. However, due to the strong influence of a tip-dependent background on these peaks. the corresponding surface state energies cannot be found directly from those curves. The real surface state energies were recovered by normalizing the measured dI/dV curves by fitted quadratic backgrounds. Thus, surface state energies of about +0.35 and +0.25 eV are estimated for pure Mn islands and alloyed MnFe areas, respectively. (C) 2002 Elsevier Science B.V. All rights reserved.
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  • MMJ Bischoff, T Yamada, AJ Quinn, RGP van der Kraan, H van Kempen
    PHYSICAL REVIEW LETTERS 87(24) 246102-1 2001年12月  査読有り
    Scanning tunneling microscopy studies on the growth of Au on Fe(001) are reported. A surface alloy is observed for submonolayer deposition (<0.5 monolayer) at temperatures higher than 370 K. This surface-confined alloy demixes when it is covered with Au and in combination with imperfect layer-by-layer growth a rough interface consisting of Au islands in and Fe islands on the original Fe(001) substrate is created. A real-space high resolution study of this buried interface is possible because of the large difference in interlayer spacing between bcc Fe(001) and fcc Au(001).
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  • T Yamada, J Fujii, T Mizoguchi
    SURFACE SCIENCE 479(1-3) 33-42 2001年5月  査読有り筆頭著者
    Various surface configurations of Cs/p-GaAs(1 1 0) have been studied by scanning tunneling microscopy and scanning tunneling spectroscopy with an interest in relation to the photoelectron emission. The local work function is found to be 4.8, 3.3, and 3.3 eV from clean p-GaAs(1 1 0), Cs one-dimensional (1D) lines (Cs coverage of 0.23 ML), and partially-ordered Cs polygons (Cs coverage of 0.5 ML), respectively. It is understood that only a coherently c(4 x 4)-ordered Cs-polygon surface (Cs coverage of 0.6 and 0.7 ML) can emit photoelectrons due to a sufficient reduction of the local work function down to 1.3 eV to get the negative electron affinity state. The local work function image shows that the boundary of Cs atoms has a lower local work function than at the top of Cs atoms. (C) 2001 Elsevier Science B.V. All rights reserved.
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  • T Yamada, J Fujii, T Mizoguchi
    SPIN 2000 570 908-911 2001年  
    Various stage of adsorbed Cs, i,e., one-dimensional (ID) lines, polygons and coherently c(4x4)-ordered polygons, on cleaved p-GaAs(IIO) are studied by scanning tunneling microscopy (STM) and scanning tunneling spectroscopies (STS) with an interest in relation to the photo-electron emission. It is understood that only the coherently c(4x4)-ordered Cs polygon surface (Cs coverage of 0.6ML and 0.7 ML) can emit photo-electrons due to a sufficient reduction of the local work function down to 1.3 eV to get a negative electron affinity state.
  • Y. Oshima, T. Yamada, J. Fujii, T. Mizoguchi
    Trans. Magn. Soc. Japan 1(1) 16-21 2001年  査読有り
    The saturation spin polarization of secondary electrons from a clean Ni (110) surface was quantitatively measured at 0.094 after careful calibration of a compact Mott detector installed in an Auger electron analyzer for strict inspection of the cleanness of the surface. The spin-dependent mean absorption length of Ni (110) was deduced to be about four layers of Ni (110), that is, λ+= 1.016 nm and λ _= 0.972 nm for the majority spin and minority spin electrons, respectively, from the primary electron energy dependence of the yield and the asymmetry of secondary electrons. The saturation spin polarization was reduced to 0.060, that is, 64% of that for the clean Ni (110) surface, after only 1 hour in a UHV chamber (2×10-7Pa) following a cleaning procedure, for sub-mono-layer oxygen-chemisorbed Ni (110). A model of anti-ferromagnetic Ni spin moments resulting from 180-degree super-exchange through oxygen atoms in the first layer, based on reported STM observations of Ni-O atomic arrangement, is proposed for use in further investigations to explain this drastic reduction in the polarization, which must be very sensitive to the surface magnetic configuration.
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MISC

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 18
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講演・口頭発表等

 381
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所属学協会

 10
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Works(作品等)

 28
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共同研究・競争的資金等の研究課題

 51
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