785 research outputs found
Spin-wave coupling to electromagnetic cavity fields in dysposium ferrite
Coupling of spin-waves with electromagnetic cavity field is demonstrated in
an antiferromagnet, dysprosium ferrite (DyFeO3). By measuring transmission at
0.2-0.35 THz and sweeping sample temperature, magnon-photon coupling signatures
were found at crossings of spin-wave resonances with Fabry-Perot cavity modes
formed in samples. The obtained spectra are explained in terms of classical
electrodynamics and a microscopic model.Comment: 3 pages, 2 figure
Role of the particle size polydispersity in the electrical conductivity of carbon nanotube-epoxy composites
Carbon nanotubes (CTNs) with large aspect-ratios are extensively used to
establish electrical connectedness in polymer melts at very low CNT loadings.
However, the CNT size polydispersity and the quality of the dispersion are
still not fully understood factors that can substantially alter the desired
characteristics of CNT nanocomposites. Here we demonstrate that the electrical
conductivity of polydisperse CNT-epoxy composites with purposely-tailored
distributions of the nanotube length L is a quasiuniversal function of the
first moment of L. This finding challenges the current understanding that the
conductivity depends upon higher moments of the CNT length. We explain the
observed quasiuniversality by a combined effect between the particle size
polydispersity and clustering. This mechanism can be exploited to achieve
controlled tuning of the electrical transport in general CNT nanocomposites.Comment: 9 pages, 5 figure
Electrical conductivity of multi-walled carbon nanotubes-SU8 epoxy composites
We have characterized the electrical conductivity of the composite which
consists of multi-walled carbon nanotubes dispersed in SU8 epoxy resin.
Depending on the processing conditions of the epoxy (ranging from
non-polymerized to cross-linked) we obtained tunneling and percolating-like
regimes of the electrical conductivity of the composites. We interpret the
observed qualitative change of the conductivity behavior in terms of reduced
separation between the nanotubes induced by polymerization of the epoxy matrix.Comment: 4 pages, 3 figure
Optical properties of BiTeBr and BiTeCl
We present a comparative study of the optical properties - reflectance,
transmission and optical conductivity - and Raman spectra of two layered
bismuth-tellurohalides BiTeBr and BiTeCl at 300 K and 5 K, for light polarized
in the a-b planes. Despite different space groups, the optical properties of
the two compounds are very similar. Both materials are doped semiconductors,
with the absorption edge above the optical gap which is lower in BiTeBr (0.62
eV) than in BiTeCl (0.77 eV). The same Rashba splitting is observed in the two
materials. A non-Drude free carrier contribution in the optical conductivity,
as well as three Raman and two infrared phonon modes, are observed in each
compound. There is a dramatic difference in the highest infrared phonon
intensity for the two compounds, and a difference in the doping levels. Aspects
of the strong electron-phonon interaction are identified. Several interband
transitions are assigned, among them the low-lying absorption which has
the same value 0.25 eV in both compounds, and is caused by the Rashba spin
splitting of the conduction band. An additional weak transition is found in
BiTeCl, caused by the lower crystal symmetry.Comment: Accepted in PR
Unusual Shubnikov-de Haas oscillations in BiTeCl
We report measurements of Shubnikov-de Haas (SdH) oscillations in single
crystals of BiTeCl at magnetic fields up to 31 T and at temperatures as low as
0.4 K. Two oscillation frequencies were resolved at the lowest temperatures,
Tesla and Tesla. We also measured the
infrared optical reflectance and Hall effect; we
propose that the two frequencies correspond respectively to the inner and outer
Fermi sheets of the Rashba spin-split bulk conduction band. The bulk carrier
concentration was cm and the effective
masses for the inner and for the
outer sheet. Surprisingly, despite its low effective mass, we found that the
amplitude of is very rapidly suppressed with increasing temperature,
being almost undetectable above K
Synthesis of Homogeneous Manganese-Doped Titanium Oxide Nanotubes from Titanate Precursors
We report a novel synthesis route of homogeneously manganese-doped titanium
dioxide nanotubes in a broad concentration range. The scroll-type trititanate
(H(2)Ti(3)O(7)) nanotubes prepared by hydrothermal synthesis were used as
precursors. Mn2+ ions were introduced by an ion exchange method resulting
Mn(x)H(2-x)Ti(3)O(7). In a subsequent heat-treatment they were transformed into
Mn(y)Ti(1-y)O(2) where y=x/(3+x). The state and the local environment of the
Mn2+ ions in the precursor and final products were studied by Electron Spin
Resonance (ESR) technique. It was found that the Mn2+ ions occupy two
positions: the first having an almost perfect cubic symmetry while the other is
in a strongly distorted octahedral site. The ratio of the two Mn2+ sites is
independent of the doping level and amounts to 15:85 in Mn(x)H(2-x)Ti(3)O(7)
and to 5:95 in Mn(y)Ti(1-y)O(2). SQUID magnetometry does not show long-range
magnetic order in the homogeneously Mn2+-doped nanotubes.Comment: 7 pages, 6 figure
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