2003 Fiscal Year Final Research Report Summary
Physical properties of phonons and dynamical John-Teller effect in colossal-magnetoresistance bilayer-manganite single-crystals
| Project/Area Number |
14540319
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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 |
固体物性Ⅱ(磁性・金属・低温)
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| Research Institution | Iwate University |
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Principal Investigator |
MATSUKAWA Michiaki Iwate University, Faculty of Engineering, Professor, 工学部, 助教授 (40221585)
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| Co-Investigator(Kenkyū-buntansha) |
YOSHIMOTO Noriyuki Iwate University, Faculty of Engineering, Associate Professor, 工学部, 助教授 (80250637)
YOSHIKZAWA Msahito Iwate University, Faculty of Engineering, Professor, 工学部, 教授 (30220619)
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| Project Period (FY) |
2002 – 2003
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| Keywords | bilayer perovskite manganite / colossal magnetoresistance / e_g-electron orbital / thermal conductivity / thermal expansion / John-Teller effect / polaron |
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| Research Abstract |
We have undertaken a systematic study of thermal conductivity, thermal expansion, thermoelectric power and elastic constant as a function of temperature and magnetic field for (La_<1-z>Pr_z)_<1.2>Sr_<1.8>Mn_2O_7 (z=0, 0.2, 0.4 and 0.6) single crystals.
(1) Giant magnetothermal effect, giant magnetostriction effect and giant magnetoelastic effect are observed near the metal-insulator transition temperature showing the CMR effect.
(2) The ab-plane phonon conduction is disturbed by the dynamic lattice distortion associated with polaron hopping on Mn sites. On the other hand, the typical phonon conduction observed for the end member sample Sr_3Mn_2O_7 is attributed to a reduction of the inhomogeneities in the local lattice distortions strongly coupled with small polarons. The lattice distortion due to Pr substitution and anisotropic thermal conductivity in bilayer manganites are discussed on the basis of different relaxation models of local lattice distortions in metal and insulating states proposed by Medarde et al.
(3) The giant magnetothermal effect is scaled as a function of magnetization and discussed in terms of a systematic variation of the occupation of the e_g-electron orbital states due to Pr substitution.
(4) We have investigated the time dependence of remanent magnetostriction in a (La_<1-z>Pr_z)_<1.2>Sr_<1.8>Mn_2O_7 single crystal, in order to examine the slow dynamics of lattice distortion in bilayered manganites. A competition between double exchange and Jahn-Teller type orbital-lattice interactions results in the observed lattice profile following a stretched exponential function. This finding suggests that spatial growth of the local lattice distortions coupled with e_g-electron orbital strongly correlates with the appearance of the field-induced CMR effect.
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