Neutron Scattering Measurements of Spatially Anisotropic Magnetic Exchange Interactions in Semiconducting K0.85Fe1.54Se2 (TN=280 K)

TL;DR

This study uses neutron scattering to reveal highly anisotropic magnetic exchange interactions in semiconducting K0.85Fe1.54Se2, suggesting local correlations drive antiferromagnetism rather than Fermi surface nesting.

Contribution

It provides detailed measurements of spin excitations and anisotropic exchange interactions, highlighting the role of local correlations in iron-based semiconductors.

Findings

Spin wave spectra fit Heisenberg model with anisotropic couplings

Short-range magnetic correlations observed above T_N

Anisotropic magnetic couplings are fundamental despite Fermi surface differences

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.