Tuning the magnetism of the top-layer FeAs on BaFe$_{2}$As$_{2}$(001): First-principles study

TL;DR

This study uses first-principles calculations to explore how surface termination and doping influence the magnetic order of the top-layer FeAs on BaFe₂As₂(001), revealing tunable magnetic states and distinct STM signatures.

Contribution

It demonstrates that surface termination and doping can effectively tune the magnetic order of the top-layer FeAs in BaFe₂As₂(001), providing insights into surface magnetic properties.

Findings

As-terminated surface favors staggered dimer AFM order

Ba-terminated surface favors collinear AFM order

Surface doping reduces energy differences among AFM states

Abstract

The magnetic properties of BaFe$_{2}$As$_{2}$(001) surface have been studied by using first-principles electronic structure calculations. We find that for As-terminated surface the magnetic ground state of the top-layer FeAs is in the staggered dimer antiferromagnetic (AFM) order, while for Ba-terminated surface the collinear (single stripe) AFM order is the most stable. When a certain coverage of Ba or K atoms are deposited onto the As-terminated surface, the calculated energy differences among different AFM orders for the top-layer FeAs on BaFe$_{2}$As$_{2}$(001) can be much reduced, indicating enhanced spin fluctuations. To identify the novel staggered dimer AFM order for the As termination, we have simulated the scanning tunneling microscopy (STM) image for this state, which shows a different $\sqrt{2}\times\sqrt{2}$ pattern from the case of half Ba coverage. Our results suggest: i) the magnetic properties of the top-layer FeAs on BaFe$_{2}$As$_{2}$(001) can be tuned effectively by surface doping; ii) both the surface termination and the AFM order in the top-layer FeAs can affect the STM image of BaFe$_{2}$As$_{2}$(001).