SELF-ASSEMBLY AND MAGNETISM OF NANOCLUSTER ARRAYS Axel Enders Department of Physics and Astronomy...
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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
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
[email protected]
Slide 2
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
Slide 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
Slide 4
local: Scanning Tunneling Microscopy integral: X-ray magnetic
dichroism magneto-optical Kerr effect LOCAL AND INTEGRAL
CHARACTERIZATION
Slide 5
30 nm 8 atomic rows [111] Fe ON Pt: STRUCTURAL PHASES Pt(997):
Lee, Kuhnke, Kern, Surf. Sci. 2006
Slide 6
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
Slide 7
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
Slide 8
ATOMIC WIRES AT STEP EDGES P. Gambardella, et. al, Nature 416
(2002) 301
Slide 9
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)
Slide 10
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!
Slide 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.
Slide 12
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)
Slide 13
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
Slide 14
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
Slide 15
BUFFER LAYER ASSISTED GROWTH Key references: J.H. Weaver and
G.D. Waddill, Science 251 (1991) 1444 30 K 100 K
Slide 16
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)
Slide 17
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
Slide 18
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
Slide 19
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
Slide 20
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
Slide 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)
Slide 22
Synchrotron radiation + UHV + STM + 0.3 K + 20 T !