Impact on Interface Spin Polarization of Molecular Bonding to Metallic Surfaces

We have studied the repercussion of the molecular adsorption mechanism on the electronic properties of the interface between model nonmagnetic or magnetic metallic surfaces and metallo-organic phthalocyanines molecules (Pcs). Our intertwined x-ray absorption spectroscopy experiments and computational studies reveal that manganese Pc (MnPc) is physisorbed onto a Cu(001) surface and retains the electronic properties of a free molecule. On the other hand, MnPc is chemisorbed onto Co(001), leading to a dominant direct exchange interaction between the Mn molecular site and the Co substrate. By promoting an interfacial spin-polarized conduction state on the molecule, these interactions reveal an important lever to tailor the spintronic properties of hybrid organic-metallic interfaces.

Figure 1

(a) Adsorption geometry of MnPc on an fcc (001) surface. (b) Binding energy vs MnPc distance to the Co(001) and Cu(001) surfaces. Charge density profiles [cut in a (110) plane, along the line shown in panel (a)] for (c) $\mathrm{MnPc}/\mathrm{Cu}$ and (d) $\mathrm{MnPc}/\mathrm{Co}$ in the plane perpendicular to the substrate.

Figure 2

XAS spectra at the N $K$ edge acquired at $T=300\mathrm{K}$ and $H=0$ for $\mathrm{MnPc}(1;2.5\mathrm{ML})/\mathrm{Cu}$ and $\mathrm{MnPc}(1;2.3\mathrm{ML})/\mathrm{Co}$ so as to probe (a) N $1s\to {\pi }^{*}$ and (b) N $1s\to {\sigma }^{*}$ transitions.

Figure 3

Unoccupied N PDOS for (a) $\pi$ and (b) $\sigma$ orbitals of free MnPc and ${\mathrm{H}}_2\mathrm{Pc}$ molecules, $\mathrm{MnPc}/\mathrm{Cu}$ and $\mathrm{MnPc}/\mathrm{Co}$.

Figure 4

XMCD $H$ dependence at the Mn $L_3$ edge ($E=640\mathrm{eV}$) for (a) $\mathrm{MnPc}(2.5\mathrm{ML})/\mathrm{Cu}$ and (b) $\mathrm{MnPc}(1\mathrm{ML})/\mathrm{Co}$.

Figure 5

The spin-polarized PDOS of Mn within the free MnPc molecule is compared with the Mn, N and Cu(Co) spin-polarized PDOS for MnPc on (a) Cu(001) and (b) Co(001). Inset to panel (b): spin $\uparrow$ PDOS of $\mathrm{MnPc}/\mathrm{Co}$ near $E_F$.

Figure 6

Charge density profiles over the energy range $E_F<E<E_F+0.15\mathrm{eV}$ of $\mathrm{MnPc}/\mathrm{Co}(001)$ for spin (a) $\uparrow$ and (b) $\downarrow$ charge carriers. (c) On-site DOS at the ${\mathrm{H}}_2\mathrm{Pc}/\mathrm{Co}$ and $\mathrm{MnPc}/\mathrm{Co}$ interfaces. Green arrows indicate wave function hybridization toward decay into the hypothetical Pc film. Only the central and N1 molecular sites are represented for clarity.