Low energy spin waves and magnetic interactions in SrFe2As2.
We report inelastic neutron scattering studies of magnetic excitations in antiferromagnetically ordered SrFe2As2 (T_{N}=200-220 K), the parent compound of the FeAs-based superconductors. At low temperatures (T=7 K), the magnetic spectrum S(Q,Planck's omega) consists of a Bragg peak at the elastic position (Planck's omega=0 meV), a spin gap (Delta< or =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 SrFe2As2 is therefore consistent with a first order phase transition, similar to the structural lattice distortion.
Zhao
Jun
J
Department of Physics and Astronomy, The University of Tennessee, Knoxville, TN 37996-1200, USA.
Yao
Dao-Xin
DX
Li
Shiliang
S
Hong
Tao
T
Chen
Y
Y
Chang
S
S
Ratcliff
W
W
Lynn
J W
JW
Mook
H A
HA
Chen
G F
GF
Luo
J L
JL
Wang
N L
NL
Carlson
E W
EW
Hu
Jiangping
J
Dai
Pengcheng
P