Chalcogen-height dependent magnetic interactions and magnetic order switching in FeSe$_x$Te$_{1-x}$

TL;DR

This study uses density functional calculations to show how chalcogen height influences magnetic phases in FeSe$_x$Te$_{1-x}$, revealing a switch from double-stripe to single-stripe magnetic order with Se doping.

Contribution

It uncovers the critical role of chalcogen height in determining magnetic order and provides a unified understanding of magnetism in FeSe$_x$Te$_{1-x}$ and related superconductors.

Findings

Magnetic phase stability is highly sensitive to chalcogen height.

Lowering Te height favors single-stripe magnetic order.

Magnetic susceptibility varies linearly with temperature in the single-stripe phase.

Abstract

Magnetic properties of iron chalcogenide superconducting materials are investigated using density functional calculations. We find the stability of magnetic phases is very sensitive to the height of chalcogen species from the Fe plane: while FeTe with optimized Te height has the double-stripe-type $(\pi,0)$ magnetic ordering, the single-stripe-type $(\pi,\pi)$ ordering becomes the ground state phase when Te height is lowered below a critical value by, e.g., Se doping. This behavior is understood by opposite Te-height dependences of the superexchange interaction and a longer-range magnetic interaction mediated by itinerant electrons. We also demonstrate a linear temperature dependence of the macroscopic magnetic susceptibility in the single-stripe phase in contrast to a constant behavior in the double-stripe phase. Our findings provide a comprehensive and unified view to understand the magnetism in FeSe$_x$Te$_{1-x}$ and iron pnictide superconductors.