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Phys. Rev. Lett. 94, 017206 (2005) [4 pages]

Orbital Nature of Ferromagnetic Magnons in Manganites

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Y. Endoh1,2, H. Hiraka1, Y. Tomioka3, Y. Tokura3,4, N. Nagaosa3,5, and T. Fujiwara4
1Institute for Materials Research, Tohoku University, Katahira, Sendai 980-8577, Japan
2International Institute of Advanced Studies, Kizugawa-dai, Kizucho, Kyoto, 619-0225, Japan
3Correlated Electron Research Center, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, 305-8562, Japan
4Department of Applied Physics, University of Tokyo, Hongo, Tokyo 113-8656, Japan
5CREST, Department of Applied Physics, University of Tokyo, Hongo, Tokyo 113-8656, Japan

Received 18 May 2004; published 13 January 2005

Magnon excitation in a ferromagnetic state of Sm0.55Sr0.45MnO3 located on the verge of the metal-insulator transition has been studied in terms of the neutron scattering experiment. The anomalous magnon dispersion with the zone-boundary softening is well described by the Heisenberg model with extended exchange coupling constants Js. In particular the fourth neighbor coupling J4 is as large as 0.6 times the nearest neighbor one J1. Theoretical analysis based on the local density approximation + Hubbard U band calculation reveals that this one-dimensional exchange path is due to the (3z2-r2)-type orbital correlation, in sharp contrast to previous proposals.

© 2005 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevLett.94.017206
DOI:
10.1103/PhysRevLett.94.017206
PACS:
75.30.Ds, 61.12.–q, 71.10.–w, 72.25.–b
 
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