| Project/Area Number |
17540340
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Condensed matter physics II
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| Research Institution | Sophia University |
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Principal Investigator |
KUWAHARA Hideki Sophia University, Faculty of Science and Technology, Associate Professor (90306986)
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| Co-Investigator(Kenkyū-buntansha) |
AKAHOSHI Daisuke Sophia University, Faculty of Science and Technology, Assistant Professor (90407354)
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| Project Period (FY) |
2005 – 2006
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| Project Status |
Completed (Fiscal Year 2006)
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| Budget Amount *help |
¥3,400,000 (Direct Cost: ¥3,400,000)
Fiscal Year 2006: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 2005: ¥2,000,000 (Direct Cost: ¥2,000,000)
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| Keywords | Antiferromagnetism / Transition-Metal Oxides / Ferroelectric / Spontaneous Polarization / Dielectric Constant / Magnetic Field / Spin / 4f Electron |
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| Research Abstract |
We have investigated the dielectric and magnetic properties of Eu_<0.595>Y_<0.405>MnO_3 without the presence of the 4f magnetic moments of the rare-earth ions and have found two ferroelectric phases with polarization along the a and c axes in a zero magnetic field. A magnetic-field-induced switching from one to the other ferroelectric phase took place in which the direction of ferroelectric polarization changed from the a axis to the c axis by the application of magnetic fields parallel to the a axis. In contrast to the case of TbMnO_3, in which the 4f moments of Tb^<3+> ions play an important role in such a ferroelectric phase switching, the magnetic-field-induced switching between ferroelectric phases in Eu_<0.595>Y_<0.405>MnO_3 does not originate from the magnetic transition of the rare-earth 4f moments but from that of the Mn 3d spins.
We have also investigated the role of the 4f moment on the magnetoelectric (ME) effect of orthorhombic RMnO_3 (R=rare earth ions). In order to clarify the role of the 4f moment, we prepared three samples: (Eu, Y)MnO_3 without the 4f moment, TbMnO_3 with the anisotropic 4f moment, and (Gd, Y)MnO_3 with the isotropic 4f moment. The ferroelectric behaviors of these samples are different from each other in a zero magnetic field. (Eu, Y)MnO_3 and (Gd, Y)MnO_3 show the ferroelectric polarization along the a axis in the ground state, while TbMnO_3 shows it along the c axis. Such difference may arise from the influence of the anisotropic Tb^<3+> 4f moment. The direction of the ferroelectric polarization of RMnO_3 is determined by the internal magnetic field arising from the 4f moment.
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