Scanning tunneling microscopy of surfaces of half-metals: an ab-initio study on NiMnSb(001)

TL;DR

This study uses first-principles calculations to analyze the surface electronic and topographic properties of NiMnSb(001) half-metallic surfaces, revealing loss of half-metallicity and distinct STM contrast features due to surface states.

Contribution

It provides the first ab-initio analysis of NiMnSb(001) surfaces, detailing surface relaxations, electronic structure, and expected spin-polarized STM images, highlighting surface state effects.

Findings

Half-metallicity is lost at the surfaces.

Sb atoms dominate the STM images of MnSb-terminated surfaces.

Distinct contrast and stripe patterns are observed for Ni-terminated surfaces.

Abstract

We present a first-principles study of the unreconstructed (001) surfaces of the half-metallic ferromagnet NiMnSb. Both terminations (MnSb and Ni) are considered. We find that half-metallicity is lost at the surfaces. After a discussion of the geometric relaxations and the spin-polarized surface band structure, we focus on topography images which are expected to be found with spin-polarized scanning tunneling microscopy. For the MnSb-terminated surface we find that only the Sb atoms are visible, reflecting a geometric buckling caused by relaxations. For the Ni-terminated surface we find a strong contrast between the images of forward and reverse tip-sample-bias of 0.5 eV, as well as a stripe-like image for reverse bias. We interpret these findings in terms of highly directional surface states which are formed in the spin-down gap region.