29 research outputs found
Negative Magnetoresistance in Amorphous Indium Oxide Wires
We study magneto-transport properties of several amorphous Indium oxide
nanowires of different widths. The wires show superconducting transition at
zero magnetic field, but, there exist a finite resistance at the lowest
temperature. The broadening was explained by available phase slip
models. At low field, and far below the superconducting critical temperature,
the wires with diameter equal to or less than 100 nm, show negative
magnetoresistance (nMR). The magnitude of nMR and the crossover field are found
to be dependent on both temperature and the cross-sectional area. We find that
this intriguing behavior originates from the interplay between two field
dependent contributions.Comment: 11 pages, 7 figure
Tunneling conduction in graphene/(poly)vinyl alcohol composites
Graphene/(Poly)vinyl alcohol (PVA) composite film with thickness
were synthesized by solidification of a PVA solution comprising of dispersed
graphene nanosheets. The close proximity of the graphene sheets enables the
fluctuation induced tunneling of electrons to occur from one sheet to another.
The dielectric data show that the present system can be simulated to a parallel
resistance-capacitor network. The high frequency exponent of the frequency
variation of the ac conductivity indicates that the charge carriers move in a
two-dimensional space. The sample preparation technique will be helpful for
synthesizing flexible conductors.Comment: 10 pages, 8 figure
Sensing behaviour of some nanocomposite systems
Silver nanoparticles of diameters 3.4 to 13.2 nm grown at the interfaces between silicate glass and some oxide crystallites exhibited about six orders of magnitude reduction in resistivity for a relative humidity change from 25% to 80%. Sn-SnO2 nano core-shell structure prepared within a gel-derived silica glass film by electrodeposition technique followed by heat treatment showed large change in resistivity as a function of humidity. The resistivity also changed due to gas flow of CO2, C2H5OH and NO2, respectively. The latter arose because of reduction/oxidation of Sn4+/Sn2+ species present at the shell layer of the nanostructures. Nickel nanosheets of thickness ~0.6 nm grown within the interlayer spaces of Na-4 mica crystallites showed a change of dielectric permittivity (5%) for an applied magnetic field of 1.2 Tesla. An inhomogeneous model was used to explain this behavior. Two dimensional CuO phase was grown within the channels of diameter ~5 nm of mesoporous SiO2 structure. A magnetodielectric (MD) parameter M.D. of 4.4% was obtained in this case. BaTiO3 nanoparticles of diameter ~25 nm having pores with diameter 10 nm showed multiferroic behavior which arose due to the presence of oxygen vacancies as a result of large surface area present. An M.D. parameter of 11% was found. Similarly mesoporous LiNbO3 of 10 nm diameter showed an M.D. parameter of ~4.5% at a magnetic field 1 Tesla. A giant magnetocapacitance effect with a value of 44% at 1.5 T was observed in nickel zinc ferrite (NZF) impregnated mesoporous silica. A magnetocapacitance of 51% at magnetic field 1.7 T was found in the case of nanocomposites comprising of iron ion containing silica based nanoglass and mesoporous silica. In the last two examples the behavior was explained on the basis of Catalan model of space-charge polarization with extracted values of magnetoresistance of the NZF and nanoglass phases being 58%
Quadratic to linear magnetoresistance tuning in TmB4
The change of a material's electrical resistance (R) in response to an
external magnetic field (B) provides subtle information for the
characterization of its electronic properties and has found applications in
sensor and storage related technologies. In good metals, Boltzmann's theory
predicts a quadratic growth in magnetoresistance (MR) at low B, and saturation
at high fields. On the other hand, a number of nonmagnetic materials with weak
electronic correlation and low carrier concentration for metallicity, such as
inhomogeneous conductors, semimetals, narrow gap semiconductors and topological
insulators, two-dimensional electron gas (2DEG) show positive, non-saturating
linear magnetoresistance (LMR). However, observation of LMR in single crystals
of a good metal is rare. Here we present low-temperature, angle dependent
magnetotransport in single crystals of the antiferromagnetic metal, TmB4. We
observe large, positive and anisotropic MR(B), which can be tuned from
quadratic to linear by changing the direction of the applied field. In view of
the fact that isotropic, single crystalline metals with large Fermi surface
(FS) are not expected to exhibit LMR, we attribute our observations to the
anisotropic FS topology of TmB4. Furthermore, the linear MR is found to be
temperature-independent, suggestive of quantum mechanical origin.Comment: 14 pages, 5 figures, Accepted version of PR
Magnetodielectric effect in nickel nanosheet-Na-4 mica composites
Nickel nanosheets of thickness 0.6 nm were grown within the nanochannels of
Na-4 mica template. The specimens show magnetodielectric effect at room
temperature with a change of dielectric constant as a function of magnetic
field, the electric field frequency varying from 100 to 700 kHz. A decrease of
5% in the value of dielectric constant was observed up to a field of 1.2 Tesla.
This is explained by an inhomogeneous two-component composite model as
theoretically proposed recently. The present approach will open up synthesis of
various nanocomposites for sensor applications.Comment: 11 pages, 7 figure
Probing dipole and quadrupole resonance mode in non-plasmonic nanowire using Raman spectroscopy
Electric field enhancement in semiconductor nanostructures offers a possibility to find an alternative to the metallic particles which is well known for tuning the light-matter interaction due to its strong polarizability and size-dependent surface plasmon resonance energy. Raman spectroscopy is a powerful technique to monitor the electric field as its scattering depends on the electromagnetic eigenmode of the particle. Here, we observe enhanced polarized Raman scattering from germanium nanowires of different diameters. The incident electromagnetic radiation creates a distribution of the internal electric field inside the naowires which can be enhanced by manipulating the nanowire diameter, the incident electric field and its polarization. Our estimation of the enhancement factor, including its dependence on nanowire diameter, agrees well with the Mie theory for an infinite cylinder. Furthermore, depending on diameter of nanowire and wavelength of incident radiation, polarized Raman study shows dipolar (antenna effect) and quadrupolar resonances, which has never been observed in germanium nanowire. We attempt to understand this polarized Raman behavior using COMSOL Multiphysics simulation, which suggests that the pattern observed is due to photon confinement within the nanowires. Thus, the light scattering direction can be toggled by tuning the polarization of incident excitation and diameter of non plasmonic nanowire
Enhanced magnetic anisotropy of Nickel nanosheet prepared in Na-4 mica
Nanosheets of nickel with thickness equal to 0.6 nm have been grown within
the interlayer spaces of Na-4 mica. The sheets are made up of percolative
clusters of nanodisks. Magnetization characteristics indicate a
superparamagnetic behavior with a blocking temperature of 428 K.The magnetic
anisotropy constant as extracted from the coercivity data has been found to be
higher than that of bulk nickel by two orders of magnitude. This is ascribed to
a large aspect ratio of the nickel nanophase. The Bloch exponent is also found
to be considerably different from that of bulk nickel because of a size effect.
The Bloch Equation is still found to be valid for the two dimensional
structures.Comment: 14 pages, 9 figure