### Abstract

Low-temperature spin dynamics of the double-layered perovskite (formula presented) (LSMO327) was systematically studied in a wide hole concentration range (formula presented) The spin-wave dispersion, which is almost perfectly two-dimensional, has two branches due to a coupling between layers within a double-layer. Each branch exhibits a characteristic intensity oscillation along the out-of-plane direction. We found that the in-plane spin stiffness constant and the gap between the two branches strongly depend on x. By fitting to calculated dispersion relations and cross sections assuming a Heisenberg model, we have obtained the in-plane (formula presented) intra-bilayer (formula presented) and inter-bilayer (formula presented) exchange interactions at each x. At (formula presented) (formula presented) and (formula presented) namely almost isotropic and ferromagnetic. Upon increasing x, (formula presented) rapidly approaches zero while (formula presented) increases slightly, indicating an enhancement of the planar magnetic anisotropy. At (formula presented) (formula presented) reaches (formula presented) while (formula presented) turns to (formula presented) indicating an antiferromagnetic interaction. Such a drastic change of the exchange interactions can be ascribed to the change of the relative stability of the (formula presented) and (formula presented) orbital states upon doping. However, a simple linear combination of the two states results in an orbital state with an orthorhombic symmetry, which is inconsistent with the (formula presented) tetragonal symmetry of the crystal structure. We thus propose that an “orbital liquid” state realizes in LSMO327, where the charge distribution symmetry is kept tetragonal around each Mn site. Orbital liquid states are formulated in a theoretical model which takes into account strong electron correlations. The calculated results satisfactorily explain the systematic changes of the exchange interactions in LSMO327 observed in the experiments.

Original language | English |
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Pages (from-to) | 1-10 |

Number of pages | 10 |

Journal | Physical Review B - Condensed Matter and Materials Physics |

Volume | 65 |

Issue number | 6 |

DOIs | |

Publication status | Published - 2002 |

### ASJC Scopus subject areas

- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics

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## Cite this

*Physical Review B - Condensed Matter and Materials Physics*,

*65*(6), 1-10. https://doi.org/10.1103/PhysRevB.65.064414