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@ARTICLE{Lazo:2482,
      author       = {Lazo, C. and Caciuc, V. and Hölscher, H. and Heinze, S.},
      title        = {{R}ole of tip size, orientation, and structural relaxations
                      in first principles studies of magnetic exchange force
                      microscopy and spin polarized scanning tunneling microscopy},
      journal      = {Physical review / B},
      volume       = {78},
      number       = {21},
      issn         = {1098-0121},
      address      = {College Park, Md.},
      publisher    = {APS},
      reportid     = {PreJuSER-2482},
      pages        = {214416},
      year         = {2008},
      note         = {It is our pleasure to thank S. Blugel, Y. Mokrousov, P.
                      Ferriani, A. Schwarz, U. Kaiser, R. Schmidt, and R.
                      Wiesendanger for many insightful discussions. Computations
                      were performed at the Hamburg University of Technology, the
                      Norddeutscher Verbund fur Hoch-und Hochstleistungsrechnen
                      (HLRN), and the Forschungszentrum Julich (JUMP). We
                      acknowledge financial support from the DFG (Grants No. HO
                      2237/3-1 and No. HE 3292/4-1). S. H. thanks the
                      Stifterverband fur die Deutsche Wissenschaft and the
                      Interdisciplinary Nanoscience Center Hamburg for financial
                      support.},
      abstract     = {Using first-principles calculations based on
                      density-functional theory, we investigated the exchange
                      interaction between a magnetic tip and a magnetic sample
                      which is detected in magnetic exchange force microscopy
                      (MExFM) and also occurs in spin-polarized scanning tunneling
                      microscopy (SP-STM) experiments. As a model tip-sample
                      system, we chose Fe tips and one monolayer Fe on W(001)
                      which exhibits a checkerboard antiferromagnetic structure
                      and has been previously studied with both SP-STM and MExFM.
                      We calculated the exchange forces and energies as a function
                      of tip-sample distance using different tip models ranging
                      from single Fe atoms to Fe pyramids consisting of up to
                      fourteen atoms. We find that modeling the tip by a single Fe
                      atom leads to qualitatively different tip-sample
                      interactions than using clusters consisting of several
                      atoms. Increasing the cluster size changes the calculated
                      forces, quantitatively enhancing the detectable exchange
                      forces. Rotating the tip with respect to the surface unit
                      cell has only a small influence on the tip-sample forces.
                      Interestingly, the exchange forces on the tip atoms in the
                      nearest and next-nearest layers from the apex atom are
                      non-negligible and can be opposite to that on the apex atom
                      for a small tip. In addition, the apex atom interacts not
                      only with the surface atoms underneath but also with nearest
                      neighbors in the surface. We find that structural
                      relaxations of tip and sample due to their interaction
                      depend sensitively on the magnetic alignment of the two
                      systems. As a result the onset of significant exchange
                      forces is shifted toward larger tip-sample separations which
                      facilitates their measurement in MExFM. At small tip-sample
                      separations, structural relaxations of tip apex and surface
                      atoms can either enhance or reduce the magnetic contrast
                      measured in SP-STM.},
      keywords     = {J (WoSType)},
      cin          = {IFF-1 / IAS-1 / JARA-FIT},
      ddc          = {530},
      cid          = {I:(DE-Juel1)VDB781 / I:(DE-Juel1)IAS-1-20090406 /
                      $I:(DE-82)080009_20140620$},
      pnm          = {Grundlagen für zukünftige Informationstechnologien},
      pid          = {G:(DE-Juel1)FUEK412},
      shelfmark    = {Physics, Condensed Matter},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000262244400061},
      doi          = {10.1103/PhysRevB.78.214416},
      url          = {https://juser.fz-juelich.de/record/2482},
}