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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

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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 fr Festkrperforschung Stuttgart, Germany K. Fauth, G. Schuetz (Stuttgart) S. Bornemann, H. Ebert (Muenchen) A.Buchsbaum, P. Varga (Wien) 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 fr Festkrperforschung Stuttgart, Germany K. Fauth, G. Schuetz (Stuttgart) S. Bornemann, H. Ebert (Muenchen) A.Buchsbaum, P. Varga (Wien) ACKNOWLEDGEMENT

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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

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local: Scanning Tunneling Microscopy integral: X-ray magnetic dichroism magneto-optical Kerr effect LOCAL AND INTEGRAL CHARACTERIZATION

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30 nm 8 atomic rows [111] Fe ON Pt: STRUCTURAL PHASES Pt(997): Lee, Kuhnke, Kern, Surf. Sci. 2006

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while superparamagnetic fit yields MAE and spin block size XMCD gives magnetic moments N 3.5, MAE = 0.9 meV/atom m S = 1.85 B, m L = 0.28 B 0 70 H = 1T FE IMPURITIES ON PT(111) 0.12 ML Fe 123

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Ensemble of Fe n -clusters on Pt(111) (n=1,2,3) at T=6K Correlation of anisotropy energy with anisotropy of orbital moment Simulation of magnetisation curves m(B,T,) based on ab-initio results Minar Ebert Calculation of anisotropy energy via magnetic torque T(n) Fe1Fe2Fe3 Spin 3.493.333.2 Orbit 0.440.240.16 Eur. Phys. J. D 45, 529-534 (2007) AB-INITIO MODELING

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ATOMIC WIRES AT STEP EDGES P. Gambardella, et. al, Nature 416 (2002) 301

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

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Komelj, Steiauf, Fhnle PRB 73, 134428 (2006) Co Fe SOC at Fe and Pt site Fe only Pt only strong influence of Pt on MAE in Fe wire: -large MCA -SRT into film plane SUBSTRATE-CONTROLLED CHAIN MAGNETISM easy axis ca. 80deg with respect to surface normal!

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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.

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LARGE ANISOTROPY AND INDUCED PT MOMENTS for comparison: FePt cluster layers, H C = 0.6 T for grain sizes of 4-5nm J.A.Christodoulides et al. Phys.Rev.B 68 (2003) 054428; S.Sun et al. Science 287 (2000) 1989 increased XMCD at Fe L 3 in Fe 50 Pt 50 induced moments in Pt m tot = 2.4 B MAE = 0.42 meV/atom alloy stripe T XMCD = 10K alloy magnetic field (T)

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m L : calculated (Ederer, Fhnle, 2003) ] Mertig 1995, Ravindran 2001 MAGNETIC ANISOTROPY IN 3d-5d BINARY ALLOYS 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

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9 nm W(110): Carbon induced 15 x 12 reconstruction Co on C/W(110)Fe on C/W(110) CLUSTER SELF-ASSEMBLY ON TEMPLATES

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BUFFER LAYER ASSISTED GROWTH Key references: J.H. Weaver and G.D. Waddill, Science 251 (1991) 1444 30 K 100 K

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3.9 2.8nm6.7 4.2nm9.9 7.6nm clusters of 2 ML Fe 30L 250L CONTROL OVER CLUSTER SIZE AND MAGNETISM 100 x 100nm 2 100L 1.7 ML Fe MBE grown Eur. Phys. J. D 45, 515-520 (2007)

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4.2K... on Pt(111) 5K... on Ag(111) Co clusters (0.1 ML Co / 10 L Xe) M M M SUBSTRATE-CONTROLLED CLUSTER MAGNETISM

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3 x 0.05 ML Co / 10 L Xe 3.2 nm 100 100 nm 2 after 3 subsequent cluster fabrication cycles: TOWARDS ORDERED CLUSTER LAYERS

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Prepared at T = 300 K, STM at 77 K TCPP / Ag(111) TPP / Ag(111) H2TPP: meso-tetraphenyl porphyrin H2TCPP: meso-tetracarboxyphenyl porphyrin NN Co 0.5 nm TPP / Cu(111) TPP / Ag(111) METALLO-ORGANIC STRUCTURES

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

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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)

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