共查询到20条相似文献,搜索用时 15 毫秒
1.
G. Ballentine M. Heßler M. Kinza K. Fauth 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):535-537
Fe clusters of 105±2 atoms/cluster were mass selectively deposited onto Cu(111) at cryogenic temperatures.
XMCD was used to measure temperature and direction dependent magnetization curves.
The clusters are superparamagnetic at the lowest temperature measured (10 K). Their magnetization curves are consistent with
magnetic moments of ≈2.5μB per atom which are thus enhanced over the bulk values.
Within experimental accuracy, the clusters do not present magnetocrystalline anisotropy in the temperature range
of 10 K to 60 K. 相似文献
2.
I. Popov T. Kunze S. Gemming G. Seifert 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):439-446
The preferred adsorption sites and the propensity for a self-organised growth of the molybdenum sulfide cluster Mo6S8 on the Au(111) surface are investigated by density-functional band-structure calculations with pseudopotentials and a plane
wave basis set. The quasi-cubic cluster preferentially adsorbs via a face and remains structurally intact.
It experiences a strong, mostly non-ionic attraction to the surface
at several quasi-isoenergetic adsorption positions. A scan of the potential energy surface exhibits only small barriers between
adjacent strong adsorption sites. Hence, the cluster may move in a potential well with degenerate local energy minima at room
temperature. The analysis of the electronic structure reveals a negligible
electron transfer and S-Au hybridised states, which indicate that the cluster-surface
interaction is dominated by S-Au bonds, with minor contributions from
the Mo atom in the surface vicinity. All results indicate that Mo6S8 clusters
on the Au(111) surface can undergo a template-mediated self-assembly to an ordered inorganic monolayer, which is still redox
active and may be employed as surface-active agent in the integration of noble metal and ionic or biological components within
nano-devices.
Therefore, a classical potential model was developed on the basis of the DFT data,
which allows to study larger cluster assemblies on the Au(111). 相似文献
3.
S. Bornemann J. Minár J. B. Staunton J. Honolka A. Enders K. Kern H. Ebert 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):529-534
We present results of magnetic torque calculations using the fully relativistic
spin-polarized Korringa-Kohn-Rostoker approach applied to small Co and Fe
clusters deposited on the Pt(111) surface. From the magnetic torque one can
derive amongst others the magnetic anisotropy energy (MAE). It was found that
this approach is numerically much more stable and also computationally less
demanding than using the magnetic force theorem that allows to calculate the
MAE directly. Although structural relaxation effects were not included our
results correspond reasonably well to recent experimental data. 相似文献
4.
E. Kasabova D. Alamanova M. Springborg V. G. Grigoryan 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):425-431
The soft deposition of Ni13 and Cu13 clusters on Ni(111) and Cu(111) surfaces is studied by
means of constant-energy molecular-dynamics simulations.
The atomic interactions are described by the Embedded Atom Method.
It is shown that the shape of the nickel clusters deposited on Cu(111) surfaces remains rather intact,
while the copper clusters impacting on Ni(111) surfaces collapse forming double and triple layered
products. Furthermore, it is found that for an impact energy of 0.5 eV/atom the structures of all
investigated clusters show the lowest similarity to the original structures, except for the case of
nickel clusters deposited on a Cu(111) surface. Finally, it is demonstrated that when cluster and
substrate are of different materials, it is possible to control whether the deposition results in
largely intact clusters on the substrate or in a spreading of the clusters. This separation into
hard and soft clusters can be related to the relative cohesive energy of the crystalline materials. 相似文献
5.
Equilibrium geometries, relative stabilities, and magnetic properties of small AunMn (n=1-8) clusters have been investigated using density functional theory at the PW91P86 level. It is found that Mn atoms in the ground state AunMn isomers tend to occupy the most highly coordinated position and the lowest energy structure of AunMn clusters with even n is similar to that of pure Aun+1 clusters, except for n=2. The substitution of Au atom in Aun+1 cluster by a Mn atom improves the stability of the host clusters. Maximum peaks are observed for AunMn clusters at n=2, 4 on the size dependence of second-order energy differences and fragmentation energies, implying that the two clusters possess relatively higher stability. The HOMO-LUMO energy gaps of the ground state AunMn clusters show a pronounced odd-even oscillation with the number of Au atoms, and the energy gap of Au2Mn cluster is the biggest among all the clusters. The magnetism calculations indicate that the total magnetic moment of AunMn cluster, which has a very large magnetic moment in comparison to the pure Aun+1 cluster, is mainly localized on Mn atom. 相似文献
6.
M. Opel K. -W. Nielsen S. Bauer S. T. B. Goennenwein J. C. Cezar D. Schmeisser J. Simon W. Mader R. Gross 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(4):437-444
The existence of semiconductors exhibiting long-range ferromagnetic ordering at room temperature still is controversial. One
particularly important issue is the presence of secondary magnetic phases such as clusters, segregations, etc. These are often
tedious to detect, leading to contradictory interpretations. We show that in our cobalt doped ZnO films grown homoepitaxially
on single crystalline ZnO substrates the magnetism unambiguously stems from metallic cobalt nano-inclusions. The magnetic
behavior was investigated by SQUID magnetometry, X-ray magnetic circular dichroism, and AC susceptibility measurements. The
results were correlated to a detailed microstructural analysis based on high resolution X-ray diffraction, transmission electron
microscopy, and electron-spectroscopic imaging. No evidence for carrier mediated ferromagnetic exchange between diluted cobalt
moments was found. In contrast, the combined data provide clear evidence that the observed room temperature ferromagnetic-like
behavior originates from nanometer sized superparamagnetic metallic cobalt precipitates. 相似文献
7.
J.L. Bubendorff C. Mény E. Beaurepaire P. Panissod J.P. Bucher 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(4):635-643
The crystallographic structure and morphology of electrodeposited cobalt films on Au(111) is found to be very sensitive on
the electrolyte pH value and on the overpotential applied during deposition. The samples, 2 to 500 nm thick, where characterized
by nuclear magnetic resonance (NMR), atomic force microscopy (AFM) and electron diffraction. The latter technique shows that
the Co films grow in registry with the gold underlayer, reproducing the Au(111) texture. During the first stage of growth
and depending on overpotential and pH value, either continuous hcp Co films or hcp Co islands are formed. Only the latter
growth mode leads to an out of plane magnetization with 100% of remanence. Increasing the thickness, fcc Co becomes the prevailing
phase. Eventually the fcc to hcp ratio saturates at the same value regardless the overpotential. The thickness for which the
equilibrium fcc to hcp ratio is obtained as well as the sample structure and morphology before saturation, depend strongly
on the overpotential value. In any case, the predominance of the fcc Co phase leads to an in plane magnetization of the thick
samples. This study opens up new opportunities of engineering the properties of electrodeposited cobalt films.
Received 29 February 2000 and Received in final form 3 July 2000 相似文献
8.
The effect of oxygen/cobalt off-stoichiometry upon magnetism in CaBaCo4O7 has been investigated. It is shown that the oxides CaBaCo4O7+δ and CaBaCo4−xO7−δ (0≤x≤0.20) synthesized below 1100 °C in air exhibit phase separation, where ferrimagnetic regions with TC~56 K to 64 K coexist with regions of magnetic clusters. The latter are detected from ac-susceptibility measurements, which show various frequency dependent peaks at ~14–20 K, 37 K, and 45 K, depending on the stoichiometry. The origin of this phenomenon is attributed to the great sensitivity of the material to oxidation as the synthesis of temperature is lowered, leading to the introduction of additional Co3+ cations, with respect to the ideal formula CaBaCo22+Co23+O7. This excess Co3+ tends to destroy the ferromagnetic zig-zag chains of the ferrimagnetic structure and creates various cobalt spin clusters, leading to the inherent phase separation in the samples. 相似文献
9.
Nanocrystalline cobalt ferrites were synthesized by a simple, general, one-step sol–gel auto-combustion method. An interpretation based on the measurement of the adiabatic flame temperature and the amounts of gas evolved during reaction had been proposed for the nature of combustion. The influence of annealing temperatures on the magnetic properties was investigated. The microstructure was characterized by means of X-ray diffractometer (XRD) and transmission electron microscopy (TEM). It was found that the particle size and magnetic properties of the as-prepared ferrite samples showed strong dependence on the annealing temperature. The coercivity initially increased and then decreased with increasing annealing temperature whereas the particle size and saturation magnetization continuously increased. 相似文献
10.
Interfacial structures of cobalt(II) porphine (CoP) and [2,3,7,8,12,13,17,18‐octaethyl‐21H,23-H-porphine]cobalt(II) (CoOEP) have been studied on Au(111) electrode using electrochemical scanning tunneling microscopy (EC-STM), in-situ X-ray diffraction, and density functional theory (DFT) calculations. The adsorption of porphyrins affects the reconstruction of Au(111) surface. The adsorption of CoP causes a lifting of the reconstruction to a complete 1 × 1 structure of Au(111). On CoOEP modified Au(111), the unit cell periodicity of the reconstructed substrate structure expands compared with the √3 × 23 structure of bare Au(111). The same expanded substrate structure was observed on Au(111) modified with OEP without the coordinated Co ion; the coordinated metal ion of the adsorbed porphyrin molecule does not affect the substrate structure. This result indicates that the interaction of conjugated π electrons of porphyrin with the substrate is stronger than that of the coordinated Co ion. In-situ X-ray diffraction and DFT calculation support non-covalent interaction of porphyrins with the Au(111) surface. 相似文献
11.
D. Cheng S. Huang W. Wang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,39(1):41-48
We have investigated segregation phenomena in Cu–Au
bimetallic clusters with decahedral structures at 100 K and 300 K, based on
the second-moment approximation of the tight-binding (TB-SMA) potentials by
using Monte Carlo method. The simulation results indicate that there are
three regions (split, three-shell onion-like and core-shell region) at 100 K
and two regions (split and core-shell) at 300 K with the structure of
decahedral clusters, as the chemical potential difference Δμ
changes. It is found that the structure of decahedral clusters undergoes a
division into smaller clusters in the split region. In the core-shell
structure, Au atoms are enriched in surface and Cu atoms occupy the core of
the clusters because of the different surface energy of Cu and Au. The Au
atoms are enriched in the surface shell, and the Cu atoms are in the middle
shell, while a single Au atom is located in the center to form the
three-shell onion-like structure. The structure and binding energy of
smaller clusters after splitting are also discussed. The Au atoms generally
lie on the surface of the smaller clusters after splitting. 相似文献
12.
Magnetism in Rh clusters under hydrostatic deformations 总被引:1,自引:0,他引:1
E.O. Berlanga-Ramırez F. Aguilera-Granja A. Dıaz-Ortiz A. Vega 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(3):343-349
The magnetic behavior of rhodium clusters RhN (N = 4-38) under hydrostatic deformations was investigated. The starting cluster structures were obtained from an evolutionary
search algorithm applied to a Gupta potential. The spin-polarized electronic structure and related magnetic properties were
calculated using a self-consistent spd tight-binding Hamiltonian within the unrestricted Hartree-Fock approximation. The magnetic behavior was analyzed in terms
of the interdependence between the geometrical parameters and the electronic structure. Anomalous magnetic effects were found
in some cases.
Received 5 August 2002 / Received in final form 10 January 2003 Published online 4 March 2003
RID="a"
ID="a"e-mail: berlanga@dec1.ifisica.uaslp.mx 相似文献
13.
J. V. Pinto M. M. Cruz R. C. da Silva N. Franco A. Casaca E. Alves M. Godinho 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(3):253-260
The magnetic and electrical properties of Co-implanted
single crystalline TiO2 rutile are presented. For fluences of
the order of 1017 cm-2 and implantation energy of 150
keV the maximum atomic concentration of cobalt is 13 at% at a depth
of 65 nm from the surface. The as implanted single crystals exhibit
superparamagnetic behaviour attributed to the formation of nanosized
cobalt clusters. After annealing at 1073 K an anisotropic
ferromagnetic behaviour emerges with the easy magnetization axis
lying in the (001) plane of rutile. The ferromagnetic behaviour is
associated with oriented cobalt aggregates. Electrical conductivity
of the implanted samples annealed in vacuum also exhibits
anisotropic behaviour at low temperatures, but no magnetoresistive
effects were detected. 相似文献
14.
F. Hagelberg C. Xiao B. Marsen M. Lonfat P. Scheier K. Sattler 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(1):37-41
In a series of recent experiments, the HOMO-LUMO energy gaps of small Si clusters deposited on a graphite substrate have been
determined by Scanning Tunneling Microscopy (STM). The values obtained were found to be substantially smaller than the energy
gaps of corresponding passivated clusters. This work considers dimensional reduction as a possible mechanism for a sizeable
energy gap narrowing by the example of the system Si5. The impact of the graphite substrate on the deposited species is investigated in the framework of a pseudocluster model.
Received 30 November 2000 相似文献
15.
Structure and magnetism on iron oxide clusters Fe nO m ( n = 1-5): Calculation from first principles
H. Shiroishi T. Oda I. Hamada N. Fujima 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):85-88
We have studied structural and magnetic properties in
small iron oxide clusters,
FenOm (n = 1-5), by means of the
first-principles calculation based on the density functional
theory. We have used not only the usual spin polarized scheme,
but also the scheme for noncollinear magnetism to carry out
efficient optimization in magnetic structure. The result of
FeOm (m
= 1-4) is in good agreement
with the previous work. We found the stable adduct clusters in
FeO5 and FeO6. The
bridge site of oxygen atom is more favorable in energy than any
other site for the clusters of FenO
(n
=
2-5). As increasing the number of oxygen atoms, the
alignment of Fe magnetic moments changes from ferromagnetic
configuration to antiferromagnetic one at
FenOn (n
=
2-4). Received 10 September 2002 Published online 3 July
2003 相似文献
16.
M. Martins M. Reif L. Glaser W. Wurth 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):539-546
Magnetic properties of gadolinium clusters deposited on magnetic
ultrathin Fe/Cu(100) films have been measured using X-ray Magnetic
Circular Dichroism spectroscopy (XMCD). 3d↦4f as well as 4d↦4f
absorption spectra are presented and discussed. Changes in the
relative peak intensities between the monomer, dimer and the
corresponding monoxides are observed for the
multiplets. The comparison with bulk measurements and calculations
exhibit a transition from atomic like to bulk like properties. 相似文献
17.
R.-P. Methling V. Senz E.-D. Klinkenberg Th. Diederich J. Tiggesbäumker G. Holzhüter J. Bansmann K.H. Meiwes-Broer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):173-176
We have investigated the magnetic properties of mass-selected iron clusters using the Magneto-Optical Kerr effect (MOKE) in
longitudinal geometry. For the production of these clusters, a newly developed continuous arc cluster ion source (ACIS) was
applied. The source is based on cathodic arc erosion in inert gas environment and subsequent expansion into high vacuum. Its
intensity and stability allows mass selection within a wide size range. The source efficiency is demonstrated in deposition
experiments and transmission electron microscopy. For mass-selected iron particles deposited into a silver matrix we could
observe a change in the magnetic behaviour from ferromagnetism to superparamagnetism around a size of 10 nm at room temperature.
Received 1st December 2000 相似文献
18.
A. Quesada M. A. García J. de la Venta E. Fernández Pinel J. M. Merino A. Hernando 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(4):457-461
The future of the spintronic technology requires the development of magnetic semiconductor materials. Most research groups
have focused on diluted
magnetic semiconductors because of the promising theoretical predictions and
initial results. In this work, the current experimental situation of ZnO
based diluted magnetic semiconductors is presented. Recent results on
unexpected ferromagnetic-like behaviour in different nanostructures are also
revised, focusing on the magnetic properties of Au and ZnO nanoparticles
capped with organic molecules. These experimental observations of magnetism
in nanostructures without the typical magnetic atoms are discussed. The
doubts around the intrinsic origin of ferromagnetism in diluted magnetic
semiconductors along with the surprising magnetic properties in absence of
the typical magnetic atoms of certain nanostructures should make us consider
new approaches in the quest for room temperature magnetic semiconductors. 相似文献
19.
S. Duffe T. Irawan M. Bieletzki T. Richter B. Sieben C. Yin B. von Issendorff M. Moseler H. Hövel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):401-408
The low energy deposition of silver cluster cations with
561 (±5) atoms on a cold fullerene covered gold surface has
been studied both by scanning tunneling microscopy and molecular
dynamics simulation. The special properties of the
C60/Au(111) surface result in a noticeable fixation of the
clusters without a significant change of the cluster shape. Upon
heating to room temperature we observe a flattening or shrinking
of the cluster samples due to thermal activation. Similar changes were observed also for mass selected Ag clusters with other
sizes. For comparison
we also studied Ag islands of similar size, grown by low
temperature deposition of Ag atoms and subsequent annealing. A
completely different behavior is observed with much broader size
distributions and a qualitatively different response to
annealing. 相似文献
20.
J. Zhang D. Repetto V. Sessi J. Honolka A. Enders K. Kern 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):515-520
The growth and magnetism of nanometer size Fe clusters on stepped Pt surfaces is investigated by scanning tunneling microscopy
(STM) and magneto-optical Kerr effect measurements (MOKE). The clusters are formed on xenon buffer layers of varying thickness
and then brought into contact with the substrate by thermal desorption of the Xe. The cluster size is controlled by the thickness
of the Xe layer. It is found that clusters of diameter smaller than the Pt terrace width of 2 nm are aligned along the step
edges of the Pt(997), thus forming linear cluster chains. In this arrangement, the clusters are ferromagnetic with an easy
axis in the direction along the surface normal. If the cluster diameter is larger than the terrace width then the alignment
along the step edges is not observed and rather large agglomerates are found which are randomly distributed over the surface.
Despite their increased volume, such agglomerates are superparamagnetic with in-plane easy magnetization axis. The enhanced
magnetic anisotropy energy in the smallest clusters is originating from hybridization effects at the Fe-Pt interface. 相似文献