1. Exchange splitting in electronic states of single atoms and magnetic coupling in single dimers and trimers on a surface Mats Persson (1), Hyo-June Lee (2), and Wilson Ho (2) ( 1) Dept. of Applied Physics, Chalmers/Göteborg University, SWEDEN (2) Dept. of Physics and Astronomy and Dept. of Chemistry, University of California, Irvine, USA

2. Outline Non-magnetic Au atom and dimer on NiAl(110) surface Magnetic Co, Fe, Mn atoms and dimers, and Fe trimer on NiAl(110) surface Tunneling spectra with a non-magnetic tip and density functional calculations of: ______________________________________________________________________ N. Nilius, T. M. Wallis, M. Persson, and W. Ho., Phys. Rev. Lett. 90, 196103 (2003) H. J. Lee, W. Ho, and M. Persson, Phys. Rev. Lett. 92, 186802 (2004)

3. Non-magnetic Au atom and dimers on a NiAl(110) surface STS of Au adatom and ad-dimers. Density functional calculation (PAW-GGA) VASP

4. Au Adatom and Ad-dimers* * Nilius, Wallis, Persson, and Ho, Phys. Rev. Lett. 90, 196103 (2003)

5. Tunneling Spectra and Images of an Au Ad-dimer

6. Density Functional Calculations: Au Adatom and Ad-dimers PW-PAW-GGA (VASP) Adatom Ad-dimer

7. Au Adatom

8. Au Ad-dimer

9. Resonance Energy Splittings of Dimers

10. Magnetic atoms, dimers and trimer on a NiAl(110) surface* STS of Co, Fe, and Mn adatoms and ad-dimers and Fe ad-trimer Density functional calculation (PAW-GGA) VASP ___________________________________________________________ *H. J. Lee, W. Ho, and M. Persson, Phys. Rev. Lett. 92, 186802 (2004)

11. Magnetic adatoms at 17 K

12. Calculated Magnetic Adatom DOS

14. Two Level System with a Spin FerromagneticAnti FerromagneticNon-magnetic

15. Magnetic Co and Fe Addimers: LDOS Co 2 /NiAl(110)   E 0 (AFM)-E 0 (FM) = 0.42eV Strong adatom-adatom interaction Interadatom distance (d = 2.2 Å) shorter than bridge-bridge distance (2.9 Å) Fe 2 /NiAl(110) E 0 (AFM)-E 0 (FM) = 0.45eV  

16. Magnetic Mn Addimer: LDOS   E 0 (AFM)-E 0 (FM) = 0.036eV Weak adatom-adatom interaction Interadatom distance (d = 3.0 Å) close to the bridge-bridge distance (2.9 Å)

18. Magnetic Fe Ad-trimer  

19. Concluding Remarks Unoccupied Kohn-Sham states give a useful approximation and physical insights of tunneling spectra of resonances in atom nanostructures on NiAl(110) Non-Kondo resonance signatures of the spin state in magnetic adatoms, ad-dimers and ad-trimer

20. Acknowledgements Experiments: Niklas Nilius and Mitch Wallis, UC Irvine, USA Theory: Doug Mills and Ruqian Wu, UC Irvine, USA R. Bechara Muniz, Univ. Federal Fluminense, Niteroi, Brazil Funding: