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- Publisher
- American Physical Society (APS)
- Copyright
- Copyright © 2011 The American Physical Society
- ISSN
- 1098-0121
- eISSN
- 1550-235X
- DOI
- 10.1103/PhysRevB.84.184304
- Publisher site
- See Article on Publisher Site
Abstract
The structural and magnetic phase transition in A Fe 2 As 2 ( A = Sr and Eu) was investigated from the viewpoint of the Fe-specific phonon density of states, g e Fe ( E ) , utilizing 57 Fe nuclear resonant inelastic-scattering and a b i n i t i o phonon calculations. The c -axis-polarized Fe optical phonon branches in g e Fe ( E ) around 25 meV show no anomalies across the phase transition temperature, T SDW , with decreasing temperature. Meanwhile, the peak intensity in g e Fe ( E ) around 32 meV decreases and increases at 1.25 T SDW and T SDW , respectively, which originates from five optical phonon branches involving Fe and As atomic displacements in the tetragonal structure. This decrease in peak intensity of g e Fe ( E ) at 1.25 T SDW is related to the phonon branches involving atomic displacements in the a b plane. Furthermore, the average sound velocity derived from g e Fe ( E ) below 8 meV shows no temperature dependence down to T SDW , suggesting softening in some of the sound waves. Our results clearly indicate the presence of orthorhombic fluctuations below 1.25 T SDW in tetragonal A Fe 2 As 2 .
Journal
Physical Review B – American Physical Society (APS)
Published: Nov 1, 2011