Abstract
Magnon excitation in a ferromagnetic state of 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 s. In particular the fourth neighbor coupling is as large as 0.6 times the nearest neighbor one . Theoretical analysis based on the local density approximation Hubbard U band calculation reveals that this one-dimensional exchange path is due to the -type orbital correlation, in sharp contrast to previous proposals.
- Received 18 May 2004
DOI:https://doi.org/10.1103/PhysRevLett.94.017206
©2005 American Physical Society