Low energy spin waves and magnetic interactions in SrFe$_2$As$_2$

Details Low energy spin waves and magnetic interactions in SrFe$_2$As$_2$ Low energy spin waves and magnetic interactions in SrFe$_2$As$_2$

2008-08-18

arxiv.org/abs/0808.2455v2

Phys. Rev. Lett. 101, 167203 (2008)

Physics

Condensed Matter

Superconductivity

4 pages, 4 figures

Scientific paper

10.1103/PhysRevLett.101.167203

We report inelastic neutron scattering studies of magnetic excitations in antiferromagnetically ordered SrFe$_{2}$As$_{2}$ ($T_{N}=220$ K), the parent compound of the FeAs-based superconductors. At low temperatures (T=7 K), the spectrum of magnetic excitations $S(Q,\hbar \omega)$ consists of a Bragg peak at the elastic position ($\hbar \omega =0$ meV), a spin gap ($ \Delta \leq 6.5$ meV), and sharp spin wave excitations at higher energies. Based on the observed dispersion relation, we estimate the effective magnetic exchange coupling using a Heisenberg model. On warming across $T_{N} $, the low temperature spin gap rapidly closes, with weak critical scattering and spin-spin correlations in the paramagnetic state. The antiferromagnetic order in SrFe$_{2}$As$_{2}$ is therefore consistent with a first order phase transition, similar to the structural lattice distortion.

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