68 research outputs found
Resonance-like Goss-Haenchen Shift induced by nano-metal films
The influence of nano-metal films on the Goos-Haenchen shift (GHS) is
investigated. The films deposited at the total reflecting surface of a perspex
prism/air have a sheet resistance varying between Z = 25 and 3 000 Ohm. A
resonance-like enhancement of the shift and of the absorption is found for TE
polarized waves, when the sheet resistance approaches the value of the vacuum
impedance. For TM waves the influence of the metal films on the GHS is
comparatively weak. The experiments are carried out with microwaves. Keywords:
Goos-Haenchen shift; nano-metallic films, microwaves PACS: 42.25.Bs, 42.25.Gy,
42.50.-p, 73.40.GkComment: 6 pages, 4 figure
Negative magnetoresistance in the nearest-neighbour hopping conduction in granular gold film
The low temperature (0.5-55 K) conduction of semicontinuous gold film vacuum
deposited at T \approx 50 K is studied. The film is near the percolation
threshold (thickness 3.25 nm). Its resistance is extremely sensitive to the
applied voltage U. At low enough U the film behaves as an insulator
(two-dimensional granular metal). In this state the dependences R(T) \propto
\exp (1/T) (for T \leq 20 K) and R(U) \propto \exp (1/U)) (for T \leq 1 K and U
> 0.1 V) are observed. Magnetoresistance (MR) is negative and can be described
by \Delta R(H)/R(0) \propto -H^2/T. This negative MR which manifests itself for
nearest-neighbour hopping is rather uncommon and, up to now, has not been
clarified. The possible mechanisms of such case of negative MR are discussed.Comment: 9 pages, LATEX, 6 figures. To be published in Physica B. Fig.4 is JPG
file, in case of troubles with it, appeal for help and advice to:
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FePt icosahedra with magnetic cores and catalytic shells
Surprisingly oxidation resistant icosahedral FePt nanoparticles showing hard-magnetic properties have been fabricated by an inert-gas condensation method with in-flight annealing. High-resolution transmission electron microscopy (HRTEM) images with sub-Angstrom resolution of the nanoparticle have been obtained with focal series reconstruction, revealing noncrystalline nature of the nanoparticle. Digital dark-field method combined with structure reconstruction as well as HRTEM simulations reveal that these nanoparticles have icosahedral structure with shell periodicity. Localized lattice relaxations have been studied by extracting the position of individual atomic columns with a precision of about (0.002 nm. The lattice spacings of (111) planes from the surface region to the center of the icosahedra are found to decrease exponentially with shell numbers. Computational studies and energy-filtered transmission electron microscopy analyses suggest that a Pt-enriched surface layer is energetically favored and that site-specific vacancies are formed at the edges of facettes, which was experimentally observed. The presence of the Pt-enriched shell around an Fe/Pt core explains the environmental stability of the magnetic icosahedra and strongly reduces the exchange coupling between neighboring particles, thereby possibly providing the highest packing density for future magnetic storage media based on FePt nanoparticles
Percolation in Models of Thin Film Depositions
We have studied the percolation behaviour of deposits for different
(2+1)-dimensional models of surface layer formation. The mixed model of
deposition was used, where particles were deposited selectively according to
the random (RD) and ballistic (BD) deposition rules. In the mixed one-component
models with deposition of only conducting particles, the mean height of the
percolation layer (measured in monolayers) grows continuously from 0.89832 for
the pure RD model to 2.605 for the pure RD model, but the percolation
transition belong to the same universality class, as in the 2- dimensional
random percolation problem. In two- component models with deposition of
conducting and isolating particles, the percolation layer height approaches
infinity as concentration of the isolating particles becomes higher than some
critical value. The crossover from 2d to 3d percolation was observed with
increase of the percolation layer height.Comment: 4 pages, 5 figure
Electronic transport through domain walls in ferromagnetic nanowires: Co-existence of adiabatic and non-adiabatic spin dynamics
We study the effect of a domain wall on the electronic transport in
ferromagnetic quantum wires. Due to the transverse confinement, conduction
channels arise. In the presence of a domain wall, spin up and spin down
electrons in these channels become coupled. For very short domain walls or at
high longitudinal kinetic energy, this coupling is weak, leads to very few spin
flips, and a perturbative treatment is possible. For very long domain wall
structures, the spin follows adiabatically the local magnetization orientation,
suppressing the effect of the domain wall on the total transmission, but
reversing the spin of the electrons. In the intermediate regime, we numerically
investigate the spin-dependent transport behavior for different shapes of the
domain wall. We find that the knowledge of the precise shape of the domain wall
is not crucial for determining the qualitative behavior. For parameters
appropriate for experiments, electrons with low longitudinal energy are
transmitted adiabatically while the electrons at high longitudinal energy are
essentially unaffected by the domain wall. Taking this co-existence of
different regimes into account is important for the understanding of recent
experiments.Comment: 10 pages, 6 figure
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