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Title: Close correlation between magnetic properties and the soft phonon mode of the structural transition in BaFe2As2 and SrFe2As2

Parent compounds of Fe-based superconductors undergo a structural phase transition from a tetragonal to an orthorhombic structure. We investigated the temperature dependence of the frequencies of TA phonons that extrapolate to the shear vibrational mode at the zone center, which corresponds to the orthorhombic deformation of the crystal structure at low temperatures in BaFe2As2 and SrFe2As2. We found that acoustic phonons at small wave vectors soften gradually towards the transition from high temperatures, tracking the increase of the size of slowly fluctuating magnetic domains. On cooling below the transition to base temperature the phonons harden, following the square of the magnetic moment (which we find is proportional to the anisotropy gap). Finally, our results provide evidence for close correlation between magnetic and phonon properties in Fe-based superconductors.
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [2] ;  [5] ;  [2] ;  [6]
  1. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States). Center for Neutron Research
  2. Karlsruhe Inst. of Technology (KIT) (Germany). Inst. of Solid State Physics
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Instrument and Source Division
  4. Karlsruhe Inst. of Technology (KIT) (Germany). Inst. of Solid State Physics; Alternative Energies and Atomic Energy Commission (CEA), Saclay (France). Lab. L'eon Brillouin
  5. Bhabha Atomic Research Centre (BARC), Mumbai (India). Solid State Physics Division
  6. Univ. of Colorado, Boulder, CO (United States). Dept. of Physics
Publication Date:
OSTI Identifier:
1185763
Grant/Contract Number:
AC05-00OR22725; SC0006939
Type:
Accepted Manuscript
Journal Name:
Physical Review. B, Condensed Matter and Materials Physics
Additional Journal Information:
Journal Volume: 91; Journal Issue: 13; Journal ID: ISSN 1098-0121
Publisher:
American Physical Society (APS)
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE