2007 Fiscal Year Final Research Report Summary
Magnetoelectric Effects in Ferromagnetic Oxides with the Double Perovskite Structure
| Project/Area Number |
18540342
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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 | The University of Electro-Communications |
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Principal Investigator |
ASAI Kichizo The University of Electro-Communications, Faculty of Electro-Communications, Professor (00109795)
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| Co-Investigator(Kenkyū-buntansha) |
ABE Kohji The University of Electro-Communications, Faculty of Electro-Communications, Professor (20183139)
KOBAYASHI Yoshihiko The University of Electro-Communications, Faculty of Electro-Communications, Research Associate (60293122)
SATO Keisuke FUJITSU Laboratories Ltd, Device & Materials Laboratories, Research (10418212)
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| Project Period (FY) |
2006 – 2007
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| Keywords | Ferromagnetic & ferroelectric material / Multiferroic / Magnetoelectric effect / Double perovskite structure / Superexchange interaction / Hyperfine magnetic field / NMR / Maxwell-Wagner model |
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| Research Abstract |
We have investigated (1) the crystal structure and the magnetic-dielectric properties, (2) competition of the ferromagnetism and ferroelectricity, and (3) the magnetoelectric effects of La_<1-x>Bi_xMn_<0.5>Ni_<0.5>O_3 by means of the x-ray diffraction, magnetic and electric measurements, and ^<55>Mn NMR.
(1) Polycrystalline La_<1-x>Bi_xMn_<0.5>Ni_<0.5>O_3 with the double perovskite structure has been successfully synthesized for x=0〜0.9 by soft chemical synthesis at ambient pressure. The dielectric constant increases and the ferromagnetic Curie temperature (T_<CM>) decreases with increasing x.
(2) It has been clarified through NMR of ^<55>Mn in REMn_<0.5>(Ni_<1-x>Mg_x)_<0.5>Ni_<0.5>O_3 (RE = rare earth elements) that the covalency parameter, f(RE), for Mn^<4+>-O^<2->-Ni^<2+> bond in the double perovskite is evaluated from the hyperfine magnetic field, H_<HF>, at ^<55>Mn. Based on the knowledge, the covalency parameter, f (x), for the bond in La_<1-x>Bi_xMn_<0.5>Ni_<0.5>Ni_<0.5>O_3 is fou
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nd to decrease with increasing x by ^<55>Mn NMR study of the oxides. The decrease of T_<CM> with increasing xis naturally explained with the decrease of f(x).
The decrease of f (x) is attributed to the strong covalency of Bi^<3+>-O^<2-> bond compared with La^<3+>-O^<2-> bond; more electrons of O^<2-> ions are attracted to and populate in Bi^<3+>-O^<2-> bond resulting in deficiency of electrons in Mn^<4+>-O^<2->-Ni^<2+> bond. The ferroelectricity arising from the covalency of Bi^<3+>-O^<2-> bond and the ferromagnetism arising from that of Mn^<4+>-O^<2->-Ni^<2+> bond compete with each other through the competition of the covalencies of both bonds.
(3) For x≧0.5, the dielectric constant increases in a magnetic field near T_<CM>. For x=0.7, the increment of the dielectric constant amounts to 7% at T_<CM> in 9 T. The temperature and the magnetic field dependence of the dielectric constant, including the frequency dispersion, has interpreted based on the Maxwell-Wagner model assuming an inhomogeneity of the sample which contains domains with relatively high dielectric constant dispersed in the material with negative magneto-resistance. Less
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