TY - JOUR
T1 - In-plane spin excitation anisotropy in the paramagnetic state of NaFeAs
AU - Song, Yu
AU - Regnault, Louis Pierre
AU - Zhang, Chenglin
AU - Tan, Guotai
AU - Carr, Scott V.
AU - Chi, Songxue
AU - Christianson, A. D.
AU - Xiang, Tao
AU - Dai, Pengcheng
PY - 2013/10/17
Y1 - 2013/10/17
N2 - We use unpolarized and polarized inelastic neutron scattering to study low-energy spin excitations in NaFeAs, which exhibits a tetragonal-to- orthorhombic lattice distortion at Ts≈58 K followed by a collinear antiferromagnetic (AF) order below TN≈45 K. In the AF ordered state (TN), spin waves are entirely c-axis polarized below ∼10 meV, exhibiting a gap of ∼4 meV at the AF zone center and disperse to ∼7 meV near the c-axis AF zone boundary. On warming to the paramagnetic state with orthorhombic lattice distortion (TNs), spin excitations become anisotropic within the FeAs plane. Upon further warming to the paramagnetic tetragonal state (T>Ts), spin excitations become more isotropic. Since similar magnetic anisotropy is also observed in the paramagnetic tetragonal phase of superconducting BaFe 1.904Ni0.096As2, our results suggest that the spin excitation anisotropy in superconducting iron pnictides originates from similar anisotropy already present in their parent compounds.
AB - We use unpolarized and polarized inelastic neutron scattering to study low-energy spin excitations in NaFeAs, which exhibits a tetragonal-to- orthorhombic lattice distortion at Ts≈58 K followed by a collinear antiferromagnetic (AF) order below TN≈45 K. In the AF ordered state (TN), spin waves are entirely c-axis polarized below ∼10 meV, exhibiting a gap of ∼4 meV at the AF zone center and disperse to ∼7 meV near the c-axis AF zone boundary. On warming to the paramagnetic state with orthorhombic lattice distortion (TNs), spin excitations become anisotropic within the FeAs plane. Upon further warming to the paramagnetic tetragonal state (T>Ts), spin excitations become more isotropic. Since similar magnetic anisotropy is also observed in the paramagnetic tetragonal phase of superconducting BaFe 1.904Ni0.096As2, our results suggest that the spin excitation anisotropy in superconducting iron pnictides originates from similar anisotropy already present in their parent compounds.
UR - http://www.scopus.com/inward/record.url?scp=84886666394&partnerID=8YFLogxK
U2 - 10.1103/PhysRevB.88.134512
DO - 10.1103/PhysRevB.88.134512
M3 - Article
AN - SCOPUS:84886666394
SN - 1098-0121
VL - 88
JO - Physical Review B - Condensed Matter and Materials Physics
JF - Physical Review B - Condensed Matter and Materials Physics
IS - 13
M1 - 134512
ER -