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Low energy spin waves and magnetic interactions in SrFe2As2
Jun Zhao1, Dao-Xin Yao, Shiliang Li
1Department of Physics and Astronomy, The University of Tennessee, Knoxville, TN 37996-1200, USA.
Physical Review Letters
|November 13, 2008
Summary
We studied magnetic excitations in SrFe2As2 using neutron scattering. The spin gap closes rapidly above the antiferromagnetic transition, indicating a first-order phase transition.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Magnetism
Background:
- SrFe2As2 is the parent compound for FeAs-based superconductors.
- Understanding its magnetic properties is crucial for superconductor development.
- Antiferromagnetic order exists in SrFe2As2 with a transition temperature (T_N) of 200-220 K.
Purpose of the Study:
- To investigate magnetic excitations in antiferromagnetically ordered SrFe2As2.
- To characterize the spin gap and spin-wave excitations.
- To determine the nature of the magnetic phase transition.
Main Methods:
- Inelastic neutron scattering (INS) studies.
- Analysis of the magnetic spectrum S(Q, omega) at various temperatures.
- Estimation of magnetic exchange coupling using a Heisenberg model.
Main Results:
- At low temperatures (7 K), a spin gap (Delta <= 6.5 meV) and sharp spin-wave excitations were observed.
- The spin gap rapidly closes upon warming across T_N.
- Weak critical scattering and spin-spin correlations were present in the paramagnetic state.
Conclusions:
- The magnetic excitations and spin gap behavior are consistent with a first-order phase transition.
- This transition is similar to the structural lattice distortion observed in SrFe2As2.
- The findings provide insights into the magnetic interactions governing FeAs-based materials.
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