Layer-dependent properties and noncollinear spin structure of epitaxial antiferromagnetic Mn films onCo/Cu(001)

Abstract

The surface of expanded face-centered tetragonal antiferromagnetic Mn films of a few atomic monolayers thickness grown epitaxially on $\mathrm{Co}/\mathrm{Cu}(001)$ was investigated at room temperature by scanning tunneling microscopy and scanning tunneling spectroscopy using a ferromagnetic ring-shaped bulk iron probe. We show that the main contribution to the contrast modulation observed as a function of Mn thickness in differential conductance maps is not due to spin-polarized tunneling from a layerwise antiferromagnetic spin alignment. Instead, it is mainly of electronic origin resulting from layer-dependent electronic properties of the Mn film, probably related to different levels of intermixing with Co atoms. On the atomic scale, the Mn surface demonstrates a geometrical reconstruction with a $(12\ifmmode\times\else\texttimes\fi{}2)$ periodicity in two orthogonal domains on the fourfold symmetric substrate with an apparent surface corrugation of up to 0.3 \AA{}. Simultaneously recorded differential conductance maps show different textures in the two orthogonal domains, providing evidence for noncollinearity in the Mn surface spin structure.