Anisotropic itinerant magnetism and spin fluctuations in BaFe 2 As 2 : A neutron scattering study

摘要: Neutron scattering measurements were performed to investigate magnetic excitations in a single-crystal sample of the ternary iron arsenide ${\text{BaFe}}_{2}{\text{As}}_{2}$, parent compound recently discovered family Fe-based superconductors. In ordered state, we observe low energy spin-wave with gap $\ensuremath{\Delta}=9.8(4)\text{ }\text{meV}$. The in-plane velocity ${v}_{ab}$ and out-of-plane ${v}_{c}$ measured at 12 meV are 280(150) $57(7)\text{ }\text{meV}\text{ }\text{\AA{}}$, respectively. At high energy, anisotropic centered antiferromagnetic wave vectors. This indicates two-dimensional spin dynamics, which possibly exist inside Stoner continuum. ${T}_{N}=136(1)\text{ }\text{K}$, closes quasielastic is observed above ${T}_{N}$, indicative short-range fluctuations. paramagnetic intensity along $L$ direction becomes ``rodlike,'' characteristic uncorrelated spins, attesting two-dimensionality system.