Magnetic anisotropic energy gap and low energy spin wave excitation in antiferromagnetic block phase of K2Fe4Se5

摘要

Neutron scattering experiments were performed to investigate magnetic orderand magnetic excitations in ternary iron chalcogenide K2Fe4Se5. The formationof a superlattice structure below 580 K together with the decoupling betweenthe Fe-vacancy order-disorder transition and the antiferromagnetic ordertransition appears to be a common feature in the A2Fe4Se5 family. The study ofspin dynamics of K2Fe4Se5 reveals two distinct energy gaps at the magneticBrillouin zone center, which indicates the presence of magnetic anisotropy andthe decrease of local symmetry due to electronic and orbital anisotropy. Thelow-energy spin wave excitations of K2Fe4Se5 can be properly described bylinear spin wave theory within a Heisenberg model. Compared to iron pnictides,K2Fe4Se5 exhibits a more two-dimensional magnetism as characterized by largedifferences not only between out-of-plane and in-plane spin wave velocities,but also between out-of-plane and in-plane exchange interactions.