Ferromagnet/Organic Interfaces

L. G. Wang, S. S. Jaswal and E. Y. Tsymbal

in collaboration with P.A. Dowben (UNL) and A. N. Caruso (NDSU)

The atomic and electronic structure of the ferromagnet/organic interface and the effect of the organic layer on magnetic properties of the ferromagnetic electrodes in spin-electronic devices is to be studied theoretically within first-principle band structure methods and linked to experimental investigations. Funded by NSF-MRSEC and NRI.

Nugget

Density-functional calculations have been performed to study adsorption structure and binding of methanethiol, CH3S, on Co(0001) and Au(111) surfaces. These results are correlated with experimental studies performed by Dowben’s group. For the Co surface we find that the absorption of CH3S at the three-fold fcc and hcp hollow sites is most stable. For the (√3x√3)R30°, (2x2), and (2x3) adsorptions the S-C bond is normal to the surface, whereas for the (2x1) adsorption the S-C bond tilts away from the surface normal direction by ~40°. The adsorption energy is reduced with the increasing coverage which is attributed to the repulsive interaction between the adsorbates. We find that there is a large charge transfer from the substrate surface atoms to S atoms making the S-Co bond strongly polar. S atoms acquire a small magnetic moment of 0.2µB. We have also compared the adsorption geometry and electronic structure of CH3S, on Co and Au surfaces. We find that the thiol-terminated molecules bind stronger with cobalt than gold surfaces which is consistent with the experimental results.

Figure: Atomic structure of CH3S adsorbed at the hcp hollow site of the Co(0001) surface (top view), (b) total valence electron density, and (c) difference electron density reflecting the bonding of CH3S and Co surface.

Papers:

L. G. Wang, E. Y. Tsymbal, and S. S. Jaswal, “First-principles study of adsorption of methanethiol on Co(0001)”, Physical Review B 70, 075410 (2004).

L. G. Wang, E. Y. Tsymbal, and S. S. Jaswal, “ Structural and magnetic properties of clean and methylthiolate-adsorbed Co (0001) surfaces: a first-principles study”, J. Magn. Magn. Mater. 286, 119 (2005).

A. N. Caruso, L. G. Wang, S. S. Jaswal, E. Y. Tsymbal, and P. A. Dowben, “The interface electronic structure of thiol terminated molecules on cobalt and gold surfaces”, J. Mater. Science, on-line.