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Self-assembLY And Magnetism of nanocluster arrays

Self-assembLY And Magnetism of nanocluster arrays. Axel Enders Department of Physics and Astronomy and Nebraska Center for Materials and Nanoscience University of Nebraska, Lincoln, NE 68588 a.enders@me.com. Acknowledgement. R. Skomski , G. Rojas , X. Chen J.-S. Kim, J. Kim

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Self-assembLY And Magnetism of nanocluster arrays

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  1. Self-assembLY And Magnetism of nanoclusterarrays Axel Enders Department of Physics and Astronomy and Nebraska Center for Materials and Nanoscience University of Nebraska, Lincoln, NE 68588 a.enders@me.com

  2. Acknowledgement R. Skomski, G. Rojas, X. Chen J.-S. Kim, J. Kim University of Nebraska – Lincoln J. Zhang, V. Sessi, J. Honolka, I. Brihuega, C. Michaelis, and K. Kern Max-Planck-Institut für Festkörperforschung Stuttgart, Germany K. Fauth, G. Schuetz (Stuttgart) S. Bornemann, H. Ebert (Muenchen) Buchsbaum, P. Varga (Wien)

  3. Outline • Self-Assembled Model Structures of Fe on Pt • Adatoms, Chains, Surface Alloys • Local Coordination, Hybridization and Magnetism • Deposited Co Clusters • Substrate-induced Anisotropy • Magnetic Moment of Rh Clusters in Contact with Surfaces • Ordering on Nanotemplates

  4. Local and integral characterization local: Scanning Tunneling Microscopy integral: X-ray magnetic dichroism magneto-optical Kerr effect

  5. Fe on Pt: structural phases 8 atomic rows [111] 30 nm Pt(997): Lee, Kuhnke, Kern, Surf. Sci. 2006

  6. Fe impurities on Pt(111) H = 1T XMCD gives magnetic moments 0° mS = 1.85µB, mL = 0.28µB 70° while superparamagnetic fit yields MAE and spin block size N  3.5, MAE = 0.9 meV/atom 0.12 ML Fe 1 2 3

  7. Ab-initio modeling Minar Ebert Calculation of anisotropy energy via magnetic torque T(n) Simulation of magnetisation curves m(B,T,θ) based on ab-initio results Correlation of anisotropy energy with anisotropy of orbital moment Ensemble of Fen-clusters on Pt(111) (n=1,2,3) at T=6K Eur. Phys. J. D 45, 529-534 (2007)

  8. Atomic wires at step edges P. Gambardella, et. al, Nature 416 (2002) 301

  9. Monowires on Pt(997) 0.1 ML Fe/Pt(997), dI/dV Magnetization at B = 1T Magnetization (a.u.) Co-measurements: P. Gambardella et al. Nature 416 (2002) 301 PRB 74, 054408 (2006)

  10. Substrate-controlled chain magnetism Komelj, Steiauf, Fähnle PRB 73, 134428 (2006) Co Fe only • strong influence of Pt on • MAE in Fe wire: • large MCA • SRT into film plane Pt only Fe SOC at Fe and Pt site easyaxis ca. 80deg with respect to surface normal!

  11. Fe-pt surface alloy Deposition of 0.5 ML Fe (a) and 0.25 ML Fe (b) on Pt(997) at 525 K Honolka, Enders, Kern, Fauth, Schuetz, Buchsbaum, Varga, Bornemann, Ebert, Skomski, PRL 2009.

  12. Large anisotropy and induced Pt moments alloy alloy stripe TXMCD = 10K magnetic field (T) increased XMCD at Fe L3 in Fe50Pt50 induced moments in Pt mtot = 2.4µB MAE = 0.42 meV/atom forcomparison: FePtclusterlayers, HC = 0.6 Tfor grain sizes of 4-5nm J.A.Christodoulides et al. Phys.Rev.B68 (2003) 054428; S.Sun et al. Science 287 (2000) 1989

  13. Magnetic anisotropy in 3d-5d binary alloys Mertig 1995, Ravindran 2001 [ DmL: calculated (Ederer, Fähnle, 2003) ] Fully relativistic ab-initio calculations on 2D alloy layers (H. Ebert): 2 x 1 alloy: strong FM coupling along wires (30meV/atom) weak FM coupling between wires (0.5 meV/atom) strong Dzyaloshinski-Moriya interaction (>1 meV) 2 x 2 alloy: 0.15 meV per Fe atom Disordered surface alloy ML: 0.09 meV per Fe atom Full Fe monolayer: 0.03 meV/ per atom, out of plane Key to large anisotropy: Fe bridging Fe chains at 0.5 - 0.6 ML coverage

  14. Cluster self-assembly on templates W(110): Carbon –induced 15 x 12 reconstruction Fe on C/W(110) Co on C/W(110) 9 nm

  15. Buffer layer assisted growth 30 K 30 K 100 K Key references: J.H. Weaver and G.D. Waddill, Science 251 (1991) 1444

  16. Control over Cluster size and magnetism 1.7 ML Fe MBE grown clusters of 2 ML Fe 3.9 ± 2.8nm 6.7 ± 4.2nm 9.9 ± 7.6nm 250L 30L 100L 100 x 100nm2 Eur. Phys. J. D 45, 515-520 (2007)

  17. Substrate-Controlled Cluster Magnetism 5K 5K 4.2K Co clusters (0.1 ML Co / 10 L Xe) M ... on Ag(111) ... on Pt(111) M M

  18. TowardsOrdered Cluster Layers 3.2 nm after 3 subsequent cluster fabrication cycles: 100  100 nm2 3 x 0.05 ML Co / 10 L Xe

  19. Metallo-organic structures TPP / Ag(111) TPP / Cu(111) H2TPP: meso-tetraphenyl porphyrin TCPP / Ag(111) TPP / Ag(111) N Co H2TCPP: meso-tetracarboxyphenyl porphyrin 0.5 nm Prepared at T = 300 K, STM at 77 K

  20. Future trends and perspectives 2020 multi-level hierarchic architectures adaptive programmed materials terra incognito 2015 quantum computation hybrid assemblies supramolecular technology quantum technology smart materials COMPLEXITY integrated nanosystems single electron (spin) technology 2010 advanced materials bio-inspired machines single-molecule sensing and devices photonics isolated nanostructures nanomedicine nanomagnetism in vivo nano-tools nanoelectronics bionanotechnology biomimetics molecular scale handling single electron & spin quantum coherence CONTROL

  21. Summary • Fe model structures on Pt: • Adatoms: out-of-plane M • Wires: in-plane M • Surface alloy: steps, DM interaction • 3d-5d hybridization determines anisotropy • Deposited compact clusters: • substrate-dependent anisotropy of Co on Pt(111), Ag(111) • Suppressed moments in Rh upon contact with Ag(111) • Cluster ordering with nanotemplates (BN nanomesh)

  22. Synchrotron radiation + UHV + STM + 0.3 K + 20 T !

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