Spin and Lattice excitations in Ferromagnetic Insulating Manganites

ORAL

Abstract

Though double-exchange interaction has been recognized as a major driving force for the couple magnetic and electronic phase transition, the nature of insulating ground state with ferromagnetic ordering in low-doping manganites is still not fully understood. Here we report on an inelastic neutron scattering study of spin and lattice excitations in the ferromagnetic insulating (FMI) phase of La$_{1-x}$Ca$_{x}$MnO$_{3}$ with x(Ca) = 0.2. Dispersion relations for both phonons and spin waves along high-symmetry directions were obtained for temperatures of 5 and 225 K, respectively. At low temperatures, our results indicate an anomalous softening and broadening of the magnons near the zone boundary, especially when the magnon energy E $\sim $ 20 meV, where a longitudinal optical phonon is present. Additional phonon and magnon branches observed will also be discussed.

*Acknowledgement: NSF DMR1005562

–

Authors

  • Dalgis Mesa

    • Dept. of Physics, Louisiana State University, Baton Rouge, LA 70802, USA

  • Jiandi Zhang

    • Louisiana State University, Baton Rouge, LA 70803, USA
    • Dept. of Physics, Louisiana State University, Baton Rouge, LA 70802, USA
    • Louisiana State University

  • Jaime Fernandez-Baca

    • Oak Ridge National Laboratory
    • Neutron Scattering Science Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA

  • Feng Ye

    • ORNL
    • Oak Ridge National Laboratory
    • Neutron Scattering Science Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA

  • Mark Hagen

    • Neutron Scattering Science Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA

  • T. Tomioka

    • National Institute of Advanced Industrial Science and Technology (AIST), Japan

  • Yoshinori Tokura

    • Tokyo Univ., JST and RIKEN
    • ERATO-MF, JST, CMRG and CERG, RIKEN-ASI, Wako 351-0198, Japan; Dep. Appl. Phys., Univ. Tokyo, Tokyo 113-8656, Japan
    • National Institute of Advanced Industrial Science and Technology (AIST), Japan