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2002 Fiscal Year Final Research Report Summary

Lattice and ultrasonic effects of orbital ordering and fluctuation

Research Project

Project/Area Number 11220205
Research Category

Grant-in-Aid for Scientific Research on Priority Areas (B)

Allocation TypeSingle-year Grants
Review Section Science and Engineering
Research InstitutionNiigata University

Principal Investigator

GOTO Terutaka  Niigata University, The Graduate School of Science and Technology, Professor, 大学院・自然科学研究科, 教授 (60134053)

Co-Investigator(Kenkyū-buntansha) KUSAKABE Koichi  Niigata University, The Graduate School of Science and Technology, Associate Professor, 大学院・自然科学研究科, 助教授 (10262164)
HASEGAWA Akira  Niigata University, President of Niigata University, President, 学長 (40004329)
NEMOTO Yuichi  Niigata University, The Graduate School of Science and Technology, Assistant, 大学院・自然科学研究科, 助手 (10303174)
IYETOMI Hiroshi  Niigata University Department of Physics Professor, 理学部, 教授 (20168090)
Project Period (FY) 1999 – 2001
Keywordsorbital ordering / quadrupole ordering / ultrasound / rare earth compound / transition metal / colossal magnetoresistanse / charge ordering
Research Abstract

In the present project we have investigated on orbital orderings and fluctuations by use of the coupling of the elastic strain of sound waves to the quadrupole of the orbital degrees of freedom. By the ultrasonic measurements, we have investigated the magnetic phase diagram of Ce_xLa_<1-x>B_6 with ヲ」_8 ground state. In the compound x=0.75 the ordered phase IV changes into the antiferro-magnetic phase III. In more diluted compounds x=0.70 and 0.65, however, the phase IV is stable down to absolute zero. The ultrasonic measurements show significant difference in low-temperature limit of C_<44>ofx=0.70, 0.65 and that of x=0.60, 0.50. We have deduced, therefore, that the compounds x=0.60 and 0.50 falls into a non-magnetic ground state showing no distinct phase transition. This is consistent with the previous specific heat measurements by Nakamura et al. In order to examine the order parameter of the phase IV, we have made thermal expansion measurements showing an expansion along the (001) d … More irection and a shrink along the(111) direction in phase IV. This result is a proof for a trigonal distortion in phase IV indicating a quadrupole ordering O_<yz>=O_<zx>=O_<xy>。・.
We。。have。。found that tetragonal ternary compounds HoB_2C_2 and DyB_2C_2 exhibit softenings in (C_<11>-C_<12>)/2, C_<44>, C_<66>. These results indicate a pseudo-triplet model consisting of E-doublet and B or A singlet is responsible for HoB_2C_2 and a pseudo-quartet model with E_<1/2> doublet and E_<3/2> doublet is for DyB_2C_2. We have also performed ultrasonic investigation on La_<1-x>Sr_xMnO_3 and Pr_xCa_<1-x>MnO_3 to investigate their orbital orderings. We have commonly observed the softening in (C_<11>-C_<12>)/2, in para-phase, where the Jahn-Teller coupling of quadrupoles O^0_2 and O^2_2 of E_g doublet is responsible. We obtained the energy gain 10。チ100K, which is considerable smaller than that in Mills' theory. The elastic softening in C_<44> due to charge ordering in Pr_xCa_<1-x>MnO_3 with x=0.50 has been found. We have successfully applied the Landau theory to explain the charge ordering of the system associated with the softening of C_<44>. Less

  • Research Products

    (12 results)

All Other

All Publications (12 results)

  • [Publications] T.Goto: "Quadrupole and lattice effects of orbitally degenerate 4f-electron system"J. Phys : Condens. Mat. 15. 1-7 (2003)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] Y.Nakanishi: "Unconventional emergence of elastic softening induced by magnetic field in the unusual heavy-fermion compound PrFe_4P_<12>"J. Phys : Condens. Mat. 14. 715-720 (2003)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] T.Goto: "Charge ordering, charge fluctuation and lattice effects in strongly correlated electron systems"Advances in Physics. Vol.52, No.2. 67-118 (2003)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] M.Akatsu: "Trigonal lattice distortion and ferro-quadrupole ordering in phase IV of Ce_xLa_<1-x>B_6 (x=0.75 and 0.70)"J. Phys. Soc. Jpn.. 72. 205-208 (2003)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] T.Yanagisawa: "Ultrasonic investigation of quadrupole ordering in HoB_2C_2"Phys. Rev. B. 67. 115129-1-115129-8 (2003)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] T.Goto: "Quadrupolar susceptibility of HoB_2C_2"J. Phys. Soc. Jpn.. 71(Suppl.). 88-90 (2002)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] T. Goto: "Quadrupole and lattice effects of orbitally degenerate 4f-electron system"J. Phys. Condens. Mat.. 15. 1-7 (2003)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] Y. Nakanishi: "Unconventicnal emergene of elastic softening iuduced by magnetic field in the unusual heavy-fermion compound PrFe_4P_<12>"J. Phys. Condens. Mat.. 14. 715-720 (2003)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] T. Goto: "Charge ordering, charge fluctuation and lattice effects in strongly correlated electron systems"Advances in Physics. Vol.52,No.2. 67-118 (2003)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] M. Akatsu: "Trigonal lattice distortion and ferro-quadrupole ordering in Phase IV of Ce_xLa_<1-x>B_6(x=0.75 and 0.70)"J. Phys. Soc. Jpn.. 72. 205-208 (2003)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] T. Yanagisawa: "Ultrasonic investigation of quadrupole ordering in HoB_2C_2"Phys. Rev. B. 67. 115129-1-8 (2003)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] T. Goto: "Quadrupolar susceptibility of HoB_2C_2"J. Phys. Soc. Jpn.. 71 Suppl.. 88-90 (2002)

    • Description
      「研究成果報告書概要(欧文)」より

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Published: 2004-04-14  

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