Manipulating magnetism and conductance of an adatom-molecule junction on a metal surface: An ab initio study

The state of the art ab initio calculations reveal the effect of a scanning tunneling microscopy tip on magnetic properties and conductance of a benzene-adatom sandwich on Cu(001). We concentrate on a benzene-Co system interacting with a Cr tip. Our studies give a clear evidence that magnetism and conductance in molecule-adatom junctions can be tailored by the STM tip. Varying the tip-substrate distance the magnetic moment of the Co adatom can be switched on/off. The interplay between spin-polarized electron transport through the junction and its magnetic properties is demonstrated. A spin-filter effect in the junction is predicted.

Figure 1

(Color online) Setup for the calculations. $H$ is the distance between the magnetic STM tip and the substrate. $l$ is the length of the tip, while $d$ is the distance between the benzene molecule and the tip apex.

Figure 2

(Color online) The PDOS of the Co, C, and Cr atoms in ${\text{C}}_6{\text{H}}_6/\text{Co}/\text{Cu}\left(001\right)$ junction at two different tip-substrate distances, $9.3\text{Å}$ and $8.1\text{Å}$. The black lines are the PDOSs at a larger tip-substrate distance $9.3\text{Å}$ and the red (dark gray) lines are the PDOSs at a closer tip-substrate distance $8.1\text{Å}$. (i) $3d$ states of the Co atom, (ii) $2p$ states of the C atoms in the benzene molecule, (iii) $3d$ states of the Cr tip apex. In (iii), the values of the PDOS in the region from $-2.0$ to $-0.5\text{eV}$ are scaled by factors 0.5 and 0.1, correspondingly.

Figure 3

(Color online) The transmission spectra for three different positions of the STM tip. Positive values related for the spin-up channel and negative correspond to the spin down.