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Title: Spin excitations used to probe the nature of exchange coupling in the magnetically ordered ground state of Pr0.5Ca0.5MnO3

We have used time-of-flight inelastic neutron scattering to measure the spin wave spectrum of the canonical half-doped manganite Pr0.5Ca0.5MnO3 in its magnetic and orbitally ordered phase. Comparison of the data, which cover multiple Brillouin zones and the entire energy range of the excitations, with several different models shows that only the CE-type ordered state provides an adequate description of the magnetic ground state, provided interactions beyond nearest neighbor are included. We are able to rule out a ground state in which there exist pairs of dimerized spins which interact only with their nearest neighbors. The Zener polaron ground state, which comprises strongly bound magnetic dimers, can be ruled out on the basis of gross features of the observed spin wave spectrum. A model with weaker dimerization reproduces the observed dispersion but can be ruled out on the basis of subtle discrepancies between the calculated and observed structure factors at certain positions in reciprocal space. Adding further neighbor interactions results in almost no dimerization, i.e. interpolating back to the CE model. These results are consistent with theoretical analysis of the degenerate double exchange model for half-doping.
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6]
  1. Science and Technology Facilities Council (STFC), Oxford (United Kingdom). Rutherford Appleton Lab., ISIS Neutron Source
  2. Science and Technology Facilities Council (STFC), Oxford (United Kingdom). Rutherford Appleton Lab., ISIS Neutron Source; London Centre for Nanotechnology, London (United Kingdom)
  3. Univ. of Bristol, Bristol (United Kingdom). H. H. Wills Physics Lab.
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Quantum Condensed Matter Division
  5. National Inst. of Advanced Industrial Science and Technology (AIST), Tsukuba (Japan). Electronics and Photonics Research Inst.
  6. Univ. of Tokyo (Japan). Dept. of Applied Physics
Publication Date:
OSTI Identifier:
Grant/Contract Number:
AC05-00OR22725; 2012/04/A/ST3/00331; EP/G0314060/1
Accepted Manuscript
Journal Name:
Physical Review B
Additional Journal Information:
Journal Volume: 94; Journal Issue: 1; Journal ID: ISSN 2469-9950
American Physical Society (APS)
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); UK Engineering and Physical Sciences Research Council (EPSRC); Polish National Science Center (NCN)
Country of Publication:
United States