71 research outputs found
Magnetic properties of single nanomagnets: EMCD on FePt nanoparticles
Energy-loss magnetic chiral dichroism (EMCD) allows for the quantification of
magnetic properties of materials at the nanometer scale. It is shown that with
the support of simulations that help to identify the optimal conditions for a
successful experiment and upon implementing measurement routines that
effectively reduce the noise floor, EMCD measurements can be pushed towards
quantitative magnetic measurements even on individual nanoparticles. With this
approach, the ratio of orbital to spin magnetic moments for the Fe atoms in a
single L ordered FePt nanoparticle is determined to be . This finding is in good quantitative agreement with the results of
XMCD ensemble measurements.Comment: 35 pages, 10 figure
Induction Mapping of the 3D-Modulated Spin Texture of Skyrmions in Thin Helimagnets
Envisaged applications of skyrmions in magnetic memory and logic devices
crucially depend on the stability and mobility of these topologically
non-trivial magnetic textures in thin films. We present for the first time
quantitative maps of the magnetic induction that provide evidence for a 3D
modulation of the skyrmionic spin texture. The projected in-plane magnetic
induction maps as determined from in-line and off-axis electron holography
carry the clear signature of Bloch skyrmions. However, the magnitude of this
induction is much smaller than the values expected for homogeneous Bloch
skyrmions that extend throughout the thickness of the film. This finding can
only be understood, if the underlying spin textures are modulated along the
out-of-plane z direction. The projection of (the in-plane magnetic induction
of) helices is further found to exhibit thickness-dependent lateral shifts,
which show that this z modulation is accompanied by an (in-plane) modulation
along the x and y directions
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Probing magnetic properties at the nanoscale: in-situ Hall measurements in a TEM
We report on advanced in-situ magneto-transport measurements in a transmission electron microscope. The approach allows for concurrent magnetic imaging and high resolution structural and chemical characterization of the same sample. Proof-of-principle in-situ Hall measurements on presumably undemanding nickel thin films supported by micromagnetic simulations reveal that in samples with non-trivial structures and/or compositions, detailed knowledge of the latter is indispensable for a thorough understanding and reliable interpretation of the magneto-transport data. The proposed in-situ approach is thus expected to contribute to a better understanding of the Hall signatures in more complex magnetic textures
Core–Shell Structuring of Pure Metallic Aerogels towards Highly Efficient Platinum Utilization for the Oxygen Reduction Reaction
The development of core-shell structures remains a fundamental challenge for pure metallic aerogels. Here we report the synthesis of PdxAu-Pt core-shell aerogels comprised of an ultrathin Pt shell and a composition-tunable PdxAu alloy core. The universality of this strategy ensures the extension of core compositions to Pd-transition metal alloys. The core-shell aerogels exhibited largely improved Pt utilization efficiency for oxygen reduction reaction and their activities show a volcano-type relationship as a function of the lattice parameter of the core substrate. The maximum mass and specific activities are 5.25 A mg-1Pt and 2.53 mA cm-2, which are 18.7 and 4.1 times higher than those of Pt/C, respectively, demonstrating the superiority of the core-shell metallic aerogels. The proposed core-based activity descriptor provides a new possible strategy for the design of future core-shell electrocatalysts
Direct Observation of Plasmon Band Formation and Delocalization in Quasi-Infinite Nanoparticle Chains
Chains of metallic nanoparticles sustain strongly confined surface plasmons
with relatively low dielectric losses. To exploit these properties in
applications,such as waveguides, the fabrication of long chains of low disorder
and a thorough understanding of the plasmon-mode properties, such as dispersion
relations, are indispensable. Here, we use a wrinkled template for directed
self-assembly to assemble chains of gold nanoparticles. With this up-scalable
method, chain lengths from two particles (140 nm) to 20 particles (1500 nm) and
beyond can be fabricated. Electron energy-loss spectroscopy supported by
boundary element simulations, finite-difference time-domain, and a simplified
dipole coupling model reveal the evolution of a band of plasmonic waveguide
modes from degenerated single-particle modes in detail. In striking difference
from plasmonic rod-like structures, the plasmon band is confined in excitation
energy, which allows light manipulations below the diffraction limit. The
non-degenerated surface plasmon modes show suppressed radiative losses for
efficient energy propagation over a distance of 1500 nm
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Graphene-Like ZnO: A Mini Review
The isolation of a single layer of graphite, known today as graphene, not only demonstrated amazing new properties but also paved the way for a new class of materials often referred to as two-dimensional (2D) materials. Beyond graphene, other 2D materials include h-BN, transition metal dichalcogenides (TMDs), silicene, and germanene, to name a few. All tend to have exciting physical and chemical properties which appear due to dimensionality effects and modulation of their band structure. A more recent member of the 2D family is graphene-like zinc oxide (g-ZnO) which also holds great promise as a future functional material. This review examines current progress in the synthesis and characterization of g-ZnO. In addition, an overview of works dealing with the properties of g-ZnO both in its pristine form and modified forms (e.g., nano-ribbon, doped material, etc.) is presented. Finally, discussions/studies on the potential applications of g-ZnO are reviewed and discussed
Monolithic growth of ultra-thin Ge nanowires on Si(001)
Self-assembled Ge wires with a height of only 3 unit cells and a length of up
to 2 micrometers were grown on Si(001) by means of a catalyst-free method based
on molecular beam epitaxy. The wires grow horizontally along either the [100]
or the [010] direction. On atomically flat surfaces, they exhibit a highly
uniform, triangular cross section. A simple thermodynamic model accounts for
the existence of a preferential base width for longitudinal expansion, in
quantitative agreement with the experimental findings. Despite the absence of
intentional doping, first transistor-type devices made from single wires show
low-resistive electrical contacts and single hole transport at sub-Kelvin
temperatures. In view of their exceptionally small and self-defined cross
section, these Ge wires hold promise for the realization of hole systems with
exotic properties and provide a new development route for silicon-based
nanoelectronics.Comment: 23 pages, 5 figure
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