2002 Fiscal Year Final Research Report Summary
Competitive Antiferroquadrupolar and Antiferromagnetic Interactions in Tetragonal Rare-earth Compounds RB_2C_2.
| Project/Area Number |
12304017
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
固体物性Ⅱ(磁性・金属・低温)
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| Research Institution | Tohoku University |
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Principal Investigator |
YAMAGUCHI Yasuo Tohoku Univ., Inst. Mater. Res., Professor, 金属材料研究所, 教授 (80005917)
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| Co-Investigator(Kenkyū-buntansha) |
OHOYAMA Kenji Tohoku Univ., Inst. Mater. Res., Research Associate, 金属材料研究所, 助手 (60241569)
ISHIMOTO Kenichi Tohoku Univ., Inst. Mater. Res., Research Associate, 金属材料研究所, 助手 (00212936)
ONODERA Hideya Tohoku Univ., Inst. Mater. Res., Associate Professor, 金属材料研究所, 助教授 (50005972)
TOBO Aya Tohoku Univ., Inst. Mater. Res., Research Associate, 金属材料研究所, 助手 (40300884)
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| Project Period (FY) |
2000 – 2002
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| Keywords | RB_2C_2 / Antiferroquadrupolar order / Antiferromagnetism / Magnetic structure / Magnetic phase diagram / Phase transition / Electric quadrupole / Magnetic dipole |
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| Research Abstract |
Growth of single crystals, identification of crystal structure and various measurements such an magnetic susceptibility, magnetization, specific heat, electric resistivity, Mossbauer effect and neutron scattering have been performed is order to clarify antiferroquadrupolar (AFQ) interaction and ordering in tetragonal RB_2C_2 compounds.
Precise magnetic phase diagrams were determined no DyB_2C_2 with an AFQ ordering temperature of T_Q=24.3 K and an antiferromagnetic (AFM) one of T_N=l5.3 K and HoB_2C_2 with the reverse transition sequence of T_N=5.8 K and T_Q=5.0 K. The AFM, AFQ or their coexistent structure in every phase was also determined by neutron diffraction on single crystals in magnetic fields. Moreover, it was revealed that anomalous phase diagrams of the AFM TbB_2C_2 with T_N=21.7 K originates in occurrence of field-induced AFQ ordering transitions, and the AFM and AFQ structures of their field-induced phases were also clarified.
The magnetic phase of T_Q≦T≦T_N in HoB_2C_2 whic
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h is adjacent to (AFM+AFQ) phase has some resemblance to that (phase IV) in cubic (Ce,La)B_6 that the character has been mysterious and controversial. It has been also found that the AFM phase of TbB_2C_2 is very similar to phase IV in the both compounds and that phase IV appears in (Dy,Gd)B_2C_2 where the transition sequence is the same to that in HoB_2C_2. Phase IV strongly attract us and is the most important target in future research in this field because of its mysterious character which might be affected strongly by octupolar interactions. Phase IV has been found in four compounds, and we found three of them in the RB_2C_2 compounds.
Combination of neutron diffraction and ^<161>Dy Mossbauer experiments gave the important information that the strong AFQ interaction mediates along the tetragonal c-axis like a pseude-one-dimmensional interaction while the AEM interactions act strongly in the C-plane. The competition of these AFQ and AFM interactions causes various and anomalous magnetic properties in RB_2C_2. Less
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