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

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)

Non-magnetic Au atom and dimers on a NiAl(110) surface

• STS of Au adatom and ad-dimers.• Density functional calculation (PAW-GGA)

VASP

Au Adatom and Ad-dimers*

* Nilius, Wallis, Persson, and Ho, Phys. Rev. Lett. 90, 196103 (2003)

Tunneling Spectra and Images of an Au Ad-dimer

Density Functional Calculations: Au Adatom and Ad-dimers

PW-PAW-GGA (VASP)

Adatom Ad-dimer

Au Adatom

Au Ad-dimer

Resonance Energy Splittings of Dimers

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)

Magnetic adatoms at 17 K

Calculated Magnetic Adatom DOS

Two Level System with a Spin

Ferromagnetic Anti FerromagneticNon-magnetic

Magnetic Co and Fe Addimers: LDOS

Co2/NiAl(110)

E0(AFM)-E0(FM) = 0.42eV

Strong adatom-adatom interaction Interadatom distance (d = 2.2 Å) shorter than bridge-bridge distance (2.9 Å)

Fe2/NiAl(110)

E0(AFM)-E0(FM) = 0.45eV

Magnetic Mn Addimer: LDOS

E0(AFM)-E0(FM) = 0.036eV

Weak adatom-adatom interaction Interadatom distance (d = 3.0 Å) close to the bridge-bridge distance (2.9 Å)

Magnetic Fe Ad-trimer

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

AcknowledgementsExperiments: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: