One-dimensional structural and electronic properties of magnetite Fe3O4(1 1 0)

We study the structure and the electronic properties of the (1 1 0) surfaces of magnetite Fe3O4 thin films by scanning tunneling microscopy (STM) and spectroscopy (STS). The STM images show a surface reconstruction consisting of ridges along the [1¯10] direction. Based on atomically resolved STM images we present a model for the observed ridge reconstruction of the surface, in agreement with a bulk-truncated layer containing both octahedral and tetrahedral iron ions. The metallic and semiconductor-like shapes of the measured current-voltage (I-V) curves indicate a non-uniform segregation of magnesium through the film. The weak contrast between the tops and valleys of ridges measured in the STS current maps is attributed to tetrahedral and octahedral coordination at the tops and the valleys, respectively. This attribution is in agreement with the proposed structure model. We observe a contrast enhancement at a tip change accompanied by a corrugation enhancement. This tip change is induced by picking up material from the sample, resulting in a magnetic tip. Thus, the contrast enhancement is attributed to detection of spin polarized current.