Magnetic excitations of small magnetic clusters and single atoms

• Applicant: Professor Dr. Wulf Wulfhekel
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2007 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 36207048

• Final Report Year: 2016

Final Report Abstract

Inelastic scanning tunneling spectroscopy (ISTS) has proven to be an excellent tool for the investigation of magnetic excitations in nanostructures allowing both to determine the excitation spectrum and the life times of the excited states. Microscopically, the interplay of spin-orbit interaction and the crystal field causes a local magnetocrystalline anisotropy (MAE). This lifts the degeneracy of the magnetic multiplet of the atom or cluster and can be probed in a spin-excitation experiment. In clusters, also non-collinear spin states can be excited with the additional cost of the exchange energy. The lifetime of the excited state is mainly determined by an electronic relaxation process, in which the energy of the excited state is given to a conduction electron of the substrate. Further the MAE induces mixing within the magnetic multiplet in accord to the Stevens operators enabling tunneling of the magnetization. For magnetic transition elements, large anisotropies of the order of 10 meV per atom could be observed, but due to the effective coupling of the atomic 3d-states to the substrate, be it metallic or a thin insulating layer, the lifetimes of the excited and ground state are between 10−14 and 10−3 s, that no magnetic stability could be achieved. In 4f-atoms, the magnetic moment is strongly located in the 4f-orbitals such that the hybridization to the surrounding states is significantly reduced. Combining this natural protection with symmetries of the Hamiltonian, stability of spins were achieved for time scales of minutes.

Publications

• Inelastic electron-magnon interaction and spin transfer torque, Phys. Rev. B 78, 174404 (2008)
  T. Balashov, A. F. Takacs, M. Dane, A. Ernst, P. Bruno, W. Wulfhekel
  
• Magnetic Anisotropy and Magnetization Dynamics of Individual Atoms and Clusters of Fe and Co on Pt(111), Phys. Rev. Lett. 102, 257203 (2009)
  T. Balashov, T. Schuh, A. F. Takacs, A. Ernst, S. Ostanin, J. Henk, I. Mertig, P. Bruno, T. Miyamachi, S. Suga, W. Wulfhekel
  
• Lifetimes of magnetic excitations in Fe and Co atoms and clusters on Pt(111), J. Appl. Phys. 107, 09E156 (2010)
  T. Schuh, T. Balashov, T. Miyamachi, A. F. Takas, S. Suga, W. Wulfhekel
  
• Magnetic anisotropy and magnetic excitations in supported atoms, Phys. Rev. B 84, 104401 (2011)
  T. Schuh, T. Balashov, T. Miyamachi, S.-Y. Wu, C.-C. Kuo, A. Ernst, J. Henk, W. Wulfhekel
  
• Magnetic Excitations of Rare Earth Atoms and Clusters on Metallic Surfaces, Nano Lett. 12, 4805-4809 (2012)
  T. Schuh, T. Miyamachi, S. Gerstl, M. Geilhufe, M. Hoffmann, S. Ostanin, W. Hergert, A. Ernst, W. Wulfhekel
  
• Parity Effect in the Ground state Localization of Antiferromagnetic Chains Coupled to a Ferromagnet, Phys. Rev. Lett. 110, 157206 (2013)
  S. Holzberger, T. Schuh, S. Blügel, S. Lounis, W. Wulfhekel
  
• Stabilizing the magnetic moment of single holmium atoms by symmetry, Nature 503, 242-246 (2013)
  T. Miyamachi, T. Schuh, T. Märkl, C. Bresch, T. Balashov, A. Stöhr, C. Karlewski, S. Andre, M. Marthaler, M. Hopffmann, M. Geilhufe, S. Ostanin, W. Hergert, I. Mertig, G. Schön, A. Ernst, W. Wulfhekel
  
• Dynamic magnetic excitations in 3d and 4f atoms and clusters, Surf. Sci. 630, 331336 (2014)
  T. Balashov, T. Miyamachi, T. Schuh, T. Markl, C. Bresch, W. Wulfhekel
  
• Magnon dispersion in thin magnetic films, J. Phys.: Condens. Matter 26 394007 (2014)
  T. Balashov, P. Buczek, L. Sandratskii, A. Ernst, W. Wulfhekel
  
• Magnetic adatoms as memory bits: A quantum master equation analysis, Phys. Rev. B 91, 245430 (2015)
  C. Karlewski, M. Marthaler, T. Märkl, T. Balashov, W. Wulfhekel, G. Schön