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


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K2Fe4Se5 compound with antiferromagnetic block structure is the parent phase of new superconducting compound KxFe2−ySe2 with TC above 30 K. Given the fact that dynamic magnetism in Fe-based superconductors may play an important role in mediating superconductivity, it is necessary to understand both static and dynamic magnetism in the insulating Fe-vacancy-ordered phase. We studied the magnetism, especially the low-energy spinwave dispersion, of a block-antiferromagnetic K2Fe4Se5 compound with both diffraction and triple-axis inelastic neutron scattering techniques.
The energy spectrum at the Brillouin zone center can be modeled with two different spin anisotropy gap parameters, which can be interpreted as indications for a breaking of local symmetry. A detailed analysis of the spin wave dispersion shows that the low-energy magnetic excitations of the antiferromagnetic block phase of K2Fe4Se5 can be well described by a Heisenberg model with local magnetic exchange couplings extended to the third-nearest neighbor. The larger energy bandwidth in K2Fe4Se5 is related to a stronger exchange coupling strength and higher antiferromagnetic transition temperature compared to other AFe2−ySe2 compounds.

Y. Xiao et al., “Magnetic anisotropic energy gap and low-energy spin wave excitation in the antiferromagnetic block phase of K2Fe4Se5” Phys. Rev. B 87, 140408(R) (2013).

Contact: Yixi Su

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