Paramagnetic spin excitations in insulating Rb₀.₈Fe₁.₆Se₂

الأصل · EN

We use neutron scattering to study temperature dependent spin excitations in insulating antiferromagnetic (AF) Rb₀.₈Fe₁.₆Se₂. In the low-temperature AF state, spin waves can be accurately described by a local moment Heisenberg Hamiltonian. On warming to around the Neel temperature of Tₙ=500 K, low-energy (E<30meV) paramagnetic spin excitations form Lorentzian-like quasielastic peaks centered at the AF wave vectors associated with spin waves, while high-energy (E>50meV) spin excitations become heavily damped. Upon further warming to above the structural distortion temperature of Tₛ=524K, the entire paramagnetic excitations become overdamped. These results suggest that AF Rb₀.₈Fe₁.₆Se₂ is not a copper-oxide-like Mott insulator, and has less electron correlations compared with metallic iron pnictides and iron chalcogenides.