Bottom-up strategies for the assembling of magnetic systems using nanoclusters
TL;DR: In this article, the authors focus on the typical case of Co clusters embedded in various matrices to study interface magnetic anisotropy and magnetic interactions as a function of volume concentrations, and illustrate size-related and nanoalloy phenomena on magnetic properties in well-defined mass-selected clusters.
Abstract: In the frame of the 20th Anniversary of the Journal of Nanoparticle Research (JNR), our aim is to start from the historical context 20 years ago and to give some recent results and perspectives concerning nanomagnets prepared from clusters preformed in the gas phase using the low-energy cluster beam deposition (LECBD) technique. In this paper, we focus our attention on the typical case of Co clusters embedded in various matrices to study interface magnetic anisotropy and magnetic interactions as a function of volume concentrations, and on still current and perspectives through two examples of binary metallic 3d-5d TM (namely CoPt and FeAu) cluster assemblies to illustrate size-related and nanoalloy phenomena on magnetic properties in well-defined mass-selected clusters. The structural and magnetic properties of these cluster assemblies were investigated using various experimental techniques that include high-resolution transmission electron microscopy (HRTEM), superconducting quantum interference device (SQUID) magnetometry, and synchrotron techniques such as extended X-ray absorption fine structure (EXAFS) and X-ray magnetic circular dichroism (XMCD). Depending on the chemical nature of both NPs and matrix, we observe different magnetic responses compared to their bulk counterparts. In particular, we show how finite size effects (size reduction) enhance their magnetic moment and how specific relaxation in nanoalloys can impact their magnetic anisotropy.
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TL;DR: Ferroelectricity in BaTiO3 crystals is used to tune the sharp metamagnetic transition temperature of epitaxially grown FeRh films and electrically drive a transition between antiferromagnetic and ferromagnetic order with only a few volts, just above room temperature, correspond to a magnetoelectric coupling larger than previous reports by at least one order of magnitude.
Abstract: Controlling magnetism by means of electric fields is a key issue for the future development of low-power spintronics1. Progress has been made in the electrical control of magnetic anisotropy2, domain structure3,4, spin polarization5,6 or critical temperatures7,8. However, the ability to turn on and o robust ferromagnetism at room temperature and above has remained elusive. Here we use ferroelectricity in BaTiO3 crystals to tune the sharp metamagnetic transition temperature of epitaxially grown FeRh films and electrically drive a transition between antiferromagnetic and ferromagnetic order with only a few volts, just above room temperature. The detailed analysis of the data in the light of first-principles calculations indicate that the phenomenon is mediated by both strain and field e ects from the BaTiO3. Our results correspond to a magnetoelectric coupling larger than previous reports by at least one order of magnitude and open new perspectives for the use of ferroelectrics in magnetic storage and spintronics.
371 citations
TL;DR: It is shown that surface segregation depends on the geometric structure, being faster in icosahedra than in fcc nanoparticles, and in the equilibration time scale, which is much longer in AgCu than in AgNi and AuCo.
Abstract: The evolution towards equilibrium of AuCo, AgNi and AgCu nanoparticles is studied by molecular dynamics simulations. Nanoparticle sizes of about 2.5 nm are considered, in the temperature range from 300 to 700 K. The simulations reveal complex equilibration pathways, in which geometric structure and chemical ordering change with time. These nanoparticles present the same type of strong tendency to phase separation and to surface segregation of either Au or Ag, which lead to the same type of core@shell equilibrium structures. In spite of these similarities, the equilibration pathways of these nanoparticles from chemically disordered configurations present both quantitative and qualitative differences. Quantitative differences are found in the equilibration time scale, which is much longer in AgCu than in AgNi and AuCo. Qualitative differences are found in the presence or absence of geometric structure transformations, and in the formation of different types of three-shell metastable chemical ordering during evolution. It is also shown that surface segregation depends on the geometric structure, being faster in icosahedra than in fcc nanoparticles.
75 citations
TL;DR: This perspective presents a review of the current research progress on the synthesis of tailored metal and metal oxide clusters including core-shell designs, their characterization within the helium droplet beam, deposition on various solid substrates, and analysis via surface diagnostics.
Abstract: Metal clusters have drawn continuous interest because of their high potential for the assembly of matter with special properties that may significantly differ from the corresponding bulk. Controlled combination of particular elements in one nanoparticle can increase the options for the creation of new materials for photonic, catalytic, or electronic applications. Superfluid helium droplets provide confinement and ultralow temperature, i.e. an ideal environment for the atom-by-atom aggregation of a new nanoparticle. This perspective presents a review of the current research progress on the synthesis of tailored metal and metal oxide clusters including core–shell designs, their characterization within the helium droplet beam, deposition on various solid substrates, and analysis via surface diagnostics. Special attention is given to the thermal properties of mixed metal clusters and questions about alloy formation on the nanoscale. Experimental results are accompanied by theoretical approaches employing computational chemistry, molecular dynamics simulations and He density functional theory.
20 citations
TL;DR: In this article, a real-time analysis of the growth of growing Co-Ag nanoparticles is performed using X-ray scattering obtained simultaneously in grazing incidence geometry (GISAXS) and GIWAXS, in single or multi-wavelength anomalous modes.
Abstract: Atomic motions and morphological evolution of growing Co–Ag nanoparticles are followed in situ and in real time, by wide and small angle X-ray scattering obtained simultaneously in grazing incidence geometry (GISAXS and GIWAXS), in single or multi-wavelength anomalous modes. The structural analysis of the experimental data is performed with the aid of equilibrium Monte Carlo simulations and of molecular-dynamics simulations of nanoparticle growth. Growth is performed by depositing Co atoms above preformed Ag nanoparticles. This growth procedure is strongly out of equilibrium, because Ag tends to surface segregation, and generates complex growth sequences. The real time analysis of the growth allows to follow the nanoparticle evolution pathways almost atom-by-atom, determining the key mechanisms during Co deposition: starting with the incorporation of Co atoms in sub-surface positions, to the off-center Co domain formation, then by which the nanoparticles finally approach their equilibrium quasi-Janus then core–shell structures.
16 citations
TL;DR: In this paper, a step-by-step analysis of CH4 dehyrogenation on 3 d 13-atom transition-metal (TM) clusters was performed using ab initio density functional theory calculations combined with Spearman rank correlation analysis and the unity bond index-quadratic exponential potential (UBI-QEP) model.
12 citations
References
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TL;DR: A software package for the analysis of X-ray absorption spectroscopy (XAS) data is presented, based on the IFEFFIT library of numerical and XAS algorithms and is written in the Perl programming language using the Perl/Tk graphics toolkit.
Abstract: A software package for the analysis of X-ray absorption spectroscopy (XAS) data is presented. This package is based on the IFEFFIT library of numerical and XAS algorithms and is written in the Perl programming language using the Perl/Tk graphics toolkit. The programs described here are: (i) ATHENA, a program for XAS data processing, (ii) ARTEMIS, a program for EXAFS data analysis using theoretical standards from FEFF and (iii) HEPHAESTUS, a collection of beamline utilities based on tables of atomic absorption data. These programs enable high-quality data analysis that is accessible to novices while still powerful enough to meet the demands of an expert practitioner. The programs run on all major computer platforms and are freely available under the terms of a free software license.
12,505 citations
TL;DR: The authors are starting to see a new paradigm where magnetization dynamics and charge currents act on each other in nanostructured artificial materials, allowing faster, low-energy operations: spin electronics is on its way.
Abstract: Electrons have a charge and a spin, but until recently these were considered separately. In classical electronics, charges are moved by electric fields to transmit information and are stored in a capacitor to save it. In magnetic recording, magnetic fields have been used to read or write the information stored on the magnetization, which 'measures' the local orientation of spins in ferromagnets. The picture started to change in 1988, when the discovery of giant magnetoresistance opened the way to efficient control of charge transport through magnetization. The recent expansion of hard-disk recording owes much to this development. We are starting to see a new paradigm where magnetization dynamics and charge currents act on each other in nanostructured artificial materials. Ultimately, 'spin currents' could even replace charge currents for the transfer and treatment of information, allowing faster, low-energy operations: spin electronics is on its way.
2,191 citations
"Bottom-up strategies for the assemb..." refers background in this paper
...Controlling nanomagnetism by means of an electric field is a key issue for the future development of low-power spintronic (Chappert et al. 2007)....
[...]
TL;DR: A new magneto-optical sum rule is derived for circular magnetic dichroism in the x-ray region (CMXD) and applications are discussed to transition-metal and rare-earth magnetic systems.
Abstract: A new magneto-optical sum rule is derived for circular magnetic dichroism in the x-ray region (CMXD). The integral of the CMXD signal over a given edge allows one to determine the ground-state expectation value of the orbital angular momentum. Applications are discussed to transition-metal and rare-earth magnetic systems.
2,041 citations
"Bottom-up strategies for the assemb..." refers background in this paper
...By applying the nowadays well-known sum rules (Carra et al. 1993, Thole et al. 1992), we determine a spin magnetic moment equal to 1.28 B per atom to compare to 1.62B per atom for the Co-bulk phase while the orbital contribution is very low 0.056 B/at to compare to the 0.15B per atom for the Cobulk…...
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TL;DR: Sum rules are derived for the circular dichroic response of a core line (CMXD) that relate the intensity of the CMXD signal to the ground-state expectation value of the magnetic field operators (orbital, spin, and magnetic dipole) of the valence electrons.
Abstract: Sum rules are derived for the circular dichroic response of a core line (CMXD). They relate the intensity of the CMXD signal to the ground-state expectation value of the magnetic field operators (orbital, spin, and magnetic dipole) of the valence electrons. The results obtained are discussed and tested for transition metals and rare earths.
1,828 citations
"Bottom-up strategies for the assemb..." refers background in this paper
...By applying the nowadays well-known sum rules (Carra et al. 1993, Thole et al. 1992), we determine a spin magnetic moment equal to 1.28 B per atom to compare to 1.62B per atom for the Co-bulk phase while the orbital contribution is very low 0.056 B/at to compare to the 0.15B per atom for the Cobulk…...
[...]
TL;DR: A method for obtaining a high-resolution image of magnetic tracers that takes advantage of the nonlinear magnetization curve of small magnetic particles and has the potential to be developed into an imaging method characterized by both high spatial resolution as well as high sensitivity.
Abstract: The use of contrast agents and tracers in medical imaging has a long history. They provide important information for diagnosis and therapy, but for some desired applications, a higher resolution is required than can be obtained using the currently available medical imaging techniques. Consider, for example, the use of magnetic tracers in magnetic resonance imaging: detection thresholds for in vitro and in vivo imaging are such that the background signal from the host tissue is a crucial limiting factor. A sensitive method for detecting the magnetic particles directly is to measure their magnetic fields using relaxometry; but this approach has the drawback that the inverse problem (associated with transforming the data into a spatial image) is ill posed and therefore yields low spatial resolution. Here we present a method for obtaining a high-resolution image of such tracers that takes advantage of the nonlinear magnetization curve of small magnetic particles. Initial 'phantom' experiments are reported that demonstrate the feasibility of the imaging method. The resolution that we achieve is already well below 1 mm. We evaluate the prospects for further improvement, and show that the method has the potential to be developed into an imaging method characterized by both high spatial resolution as well as high sensitivity.
1,774 citations