Neutron Scattering Measurements of Spatially Anisotropic Magnetic Exchange Interactions in SemiconductingK0.85Fe1.54Se2

Abstract

We use neutron scattering to study the spin excitations associated with the stripe antiferromagnetic (AFM) order in semiconducting K 0.85 Fe 1.54 Se 2 (T N =280 K). We show that the spin wave spectra can be accurately described by an effective Heisenberg Hamiltonian with highly anisotropic in-plane couplings at T = 5 K. At high temperature (T = 300 K) above T N , short range magnetic correlation with anisotropic correlation lengths are observed. Our results suggest that, despite the dramatic difference in the Fermi surface topology, the in-plane anisotropic magnetic couplings are a fundamental property of the iron based compounds; this implies that their antiferromagnetism may originate from local strong correlation effects rather than weak coupling Fermi surface nesting.

Antiferromagnetic order and spin dynamics in iron-based superconductors

“…2(e)] is the parent compound Zhao et al, 2012), one finds that spin waves of the system are rather close to those of iron pnictides. Figure 11(e), 11(f), 11(g), 11(h) shows the evolution of spin waves as a function of increasing energy for the semiconducting K 0.85 Fe 1.54 Se 2 with collinear AF order and T N = 280 K (Zhao et al, 2014). The data agrees well with calculations using a Heisenberg Hamiltonian.…”

“…The data agrees well with calculations using a Heisenberg Hamiltonian. A comparison of the observed spin wave spectrum in this system with those of the CaFe 2 As 2 single crystals ) reveals remarkable similarity, and thus suggesting similar effective magnetic exchange couplings in these systems (Zhao et al, 2014). Table II summarizes the effective magnetic exchange couplings for the parent compounds of known iron-based superconductors.…”

Strong ferromagnetic exchange interaction under ambient pressure in BaFe2S3

“…The FM J L is also contrary to a first-principles' calculation 36 , which predicts an AF J L and a FM J R . Furthermore, the inferred SJ 2 = 48.4 meV is much larger than the expectation for a superexchange interaction between two irons with the distance of 3.78Å 22,34 . Thus, the second set of parameters is unlikely to be a physical solution for the Hamiltonian for the spin waves of BaFe 2 S 3 .…”

Synthesis and Characterization of New Superconductors Materials

“…Li et al proposed that the existence of Fe vacancies could locally destroy SC [62], and suggested that the K 2 Fe 4 Se 5 layer may be indispensable to regulate superconductivity in KFe 2 Se 2 by providing charge carriers [63]. More superstructures associated with different Fe-vacancy and alkali-metal-ordering were later revealed later [64][65][66][67].…”