5.1. Nanoalloys of Group 11 (Cu, Ag, Au) 865 5.1.1. Cu−Ag 866 5.1.2. Cu−Au 867 5.1.3. Ag−Au 870 5.1.4. Cu−Ag−Au 872 5.2. Nanoalloys of Group 10 (Ni, Pd, Pt) 872 5.2.1. Ni−Pd 872 * To whom correspondence should be addressed. Phone: +39010 3536214. Fax:+39010 311066. E-mail: ferrando@fisica.unige.it. † Universita di Genova. ‡ Argonne National Laboratory. § University of Birmingham. | As of October 1, 2007, Chemical Sciences and Engineering Division. Volume 108, Number 3

Nanoalloys: From Theory to Applications of Alloy Clusters and Nanoparticles

We used a scanning tunneling microscope to probe the interactions between spins in individual atomic-scale magnetic structures. Linear chains of 1 to 10 manganese atoms were assembled one atom at a time on a thin insulating layer, and the spin excitation spectra of these structures were measured with inelastic electron tunneling spectroscopy. We observed excitations of the coupled atomic spins that can change both the total spin and its orientation. Comparison with a model spin-interaction Hamiltonian yielded the collective spin configuration and the strength of the coupling between the atomic spins.

http://science.sciencemag.org/content/sci/312/5776/1021.full.pdf

Spin coupling in engineered atomic structures.

Atomic clusters, consisting of a few to a few thousand atoms, have emerged over the past 40 years as the ultimate nanoparticles, whose structure and properties can be controlled one atom at a time. One of the early motivations in studying clusters was to understand how the properties of matter evolve as a function of size, shape, and composition. Over the past few decades, more than 200 000 papers have been published in this field. These studies have not only led to a considerable understanding of this evolution from clusters to crystals, but also have revealed many unusual size-specific properties that make cluster science an interdisciplinary field on its own, bridging physics, chemistry, materials science, biology, and medicine. More importantly, the possibility of creating a new class of materials, composed of clusters instead of atoms as building blocks, has fueled the hope that one can synthesize materials from the bottom-up with unique and tailored properties. This Review focuses on the properties ...

Super Atomic Clusters: Design Rules and Potential for Building Blocks of Materials

A study was conducted to demonstrate the manipulation of molecular beams with electric and magnetic fields. Seeded pulsed supersonic expansions were employed to conduct the investigations. The conservative forces exerted further downstream by the electric and magnetic fields enabled the researchers to manipulate and control the shape and the position of the distribution in the six-dimensional phase-space. All of the original experimental geometries were devised to create strong magnetic or electric field gradients to efficiently deflect particles from the beam axis. It was demonstrated that a detailed understanding of the influence of the external field on the energy level structure of the molecules was required for the manipulation of molecules with electric or magnetic fields.

Manipulation and control of molecular beams.

The knowledge of the atomic structure of clusters composed by few atoms is a basic prerequisite to obtain insights into the mechanisms that determine their chemical and physical properties as a function of diameter, shape, surface termination, as well as to understand the mechanism of bulk formation. Due to the wide use of metal systems in our modern life, the accurate determination of the properties of $3d$, $4d$, and $5d$ metal clusters poses a huge problem for nanoscience. In this work, we report a density functional theory study of the atomic structure, binding energies, effective coordination numbers, average bond lengths, and magnetic properties of the $3d$, $4d$, and $5d$ metal (30 elements) clusters containing 13 atoms, ${M}_{13}$. First, a set of lowest-energy local minimum structures (as supported by vibrational analysis) were obtained by combining high-temperature first-principles molecular-dynamics simulation, structure crossover, and the selection of five well-known ${M}_{13}$ structures. Several new lower energy configurations were identified, e.g., ${\text{Pd}}_{13}$, ${\text{W}}_{13}$, ${\text{Pt}}_{13}$, etc., and previous known structures were confirmed by our calculations. Furthermore, the following trends were identified: (i) compact icosahedral-like forms at the beginning of each metal series, more opened structures such as hexagonal bilayerlike and double simple-cubic layers at the middle of each metal series, and structures with an increasing effective coordination number occur for large $d$ states occupation. (ii) For ${\text{Au}}_{13}$, we found that spin-orbit coupling favors the three-dimensional (3D) structures, i.e., a 3D structure is about 0.10 eV lower in energy than the lowest energy known two-dimensional configuration. (iii) The magnetic exchange interactions play an important role for particular systems such as Fe, Cr, and Mn. (iv) The analysis of the binding energy and average bond lengths show a paraboliclike shape as a function of the occupation of the $d$ states and hence, most of the properties can be explained by the chemistry picture of occupation of the bonding and antibonding states.

Density functional theory investigation of 3d, 4d, and 5d 13-atom metal clusters

Magnetizations and magnetic moments of free cobalt clusters ${\mathrm{Co}}_{N}$ ($12lNl200$) in a cryogenic ($25\text{ }\text{ }\mathrm{K}\ensuremath{\le}T\ensuremath{\le}100\text{ }\text{ }\mathrm{K}$) molecular beam were determined from Stern-Gerlach deflections. All clusters preferentially deflect in the direction of the increasing field and the average magnetization resembles the Langevin function for all cluster sizes even at low temperatures. We demonstrate in the avoided crossing model that the average magnetization may result from adiabatic processes of rotating and vibrating clusters in the magnetic field and that spin relaxation is not involved. This resolves a long-standing problem in the interpretation of cluster beam deflection experiments with implications for nanomagnetic systems in general.

/pdf/magnetic-moments-and-adiabatic-magnetization-of-free-cobalt-hozfbdcd2n.pdf

Magnetic moments and adiabatic magnetization of free cobalt clusters.

Electric deflections of gas-phase, cryogenically cooled, neutral niobium clusters [NbN; number of atoms (N) = 2 to 150, temperature (T) = 20to 300kelvin], measured in molecular beams, show that cold clusters may attain an anomalous component with very large electric dipole moments. In contrast, room-temperature measurements show normal metallic polarizabilities. Characteristic energies kBTG(N) [Boltzmann constant kB times a transition temperature TG(N)] are identified, below which the ferroelectric-like state develops. Generally, TG decreases [110 > TG(N) > 10K] as N increases, with pronounced even-odd alternations for N > 38. This new state of metallic matter may be related to bulk superconductivity.

/pdf/ferroelectricity-in-free-niobium-clusters-1boop46oss.pdf

Ferroelectricity in free niobium clusters.

Magnetic moments of ${\mathrm{Co}}_{N}{\mathrm{Mn}}_{M}$ and ${\mathrm{Co}}_{N}{\mathrm{V}}_{M}$ clusters ($N\ensuremath{\le}60$; $M\ensuremath{\le}N/3$) are measured in molecular beams using the Stern-Gerlach deflection method. Surprisingly, the per atom average moments of ${\mathrm{Co}}_{N}{\mathrm{Mn}}_{M}$ clusters are found to increase with Mn concentration, in contrast to bulk CoMn. The enhancement with Mn doping is found to be independent of cluster size and composition in the size range studied. Meanwhile, ${\mathrm{Co}}_{N}{\mathrm{V}}_{M}$ clusters show reduction of average moments with increasing V doping, consistent with what is expected in bulk CoV. The results are discussed within the virtual bound states model.

https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1031&context=physicsxu

Magnetic enhancement in cobalt-manganese alloy clusters.

Molecular beam Stern-Gerlach deflection measurements on Nb clusters (Nb(N), N<100) show that at very low temperatures the odd-N clusters deflect due to a single unpaired spin that is uncoupled from the cluster. At higher temperatures the spin is coupled and no deflections are observed. Spin uncoupling occurs concurrently with the transition to the recently found ferroelectric state, which has superconductor characteristics [Science 300, 1265 (2003)]]. Spin uncoupling (also seen in V, Ta, and Al clusters) is analogous to the reduction of spin-relaxation rates observed in bulk superconductors below T(c).

/pdf/spin-uncoupling-in-free-nb-clusters-support-for-nascent-1yzxmtc1nn.pdf

Spin Uncoupling in Free Nb Clusters: Support for Nascent Superconductivity

Magnetic properties of free ${\mathrm{Bi}}_{N}{\mathrm{Mn}}_{M}$ clusters ($N=2--20$, $M=0--7$) are determined from Stern-Gerlach deflections at low temperature $(46.5\phantom{\rule{0.3em}{0ex}}\mathrm{K})$. Pure bismuth clusters with odd number of atoms exhibit paramagnetic deflections. The addition of manganese atoms produces a ferromagnetic response which is strongly size dependent. Certain combinations have very large magnetic moments such as ${\mathrm{Bi}}_{5}{\mathrm{Mn}}_{3}$, ${\mathrm{Bi}}_{9}{\mathrm{Mn}}_{4}$, ${\mathrm{Bi}}_{10}{\mathrm{Mn}}_{5}$, and ${\mathrm{Bi}}_{12}{\mathrm{Mn}}_{6}$.

/pdf/measurement-of-magnetic-moments-of-free-bi-n-mn-m-clusters-51y3x0jnwh.pdf

Shuangye Yin

Papers

Magnetic moments and adiabatic magnetization of free cobalt clusters.

Ferroelectricity in free niobium clusters.

Magnetic enhancement in cobalt-manganese alloy clusters.

Spin Uncoupling in Free Nb Clusters: Support for Nascent Superconductivity

Measurement of magnetic moments of free Bi N Mn M clusters