69 research outputs found
Evolution of Multipolar Magnetic Field in Isolated Neutron Stars
The evolution of the multipolar structure of the magnetic field of isolated
neutron stars is studied assuming the currents to be confined to the crust. We
find that except for multipoles of very high order (l\gsim 25) the evolution
is similar to that of a dipole. Therefore no significant evolution is expected
in pulse shape of isolated radio pulsars due to the evolution of the multipole
structure of the magnetic field.Comment: 4 pages, including 4 figures, accepted for publication M.N.R.A.
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
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
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%
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
Ferromagnetic behavior of ultrathin manganese nanosheets
Ferromagnetic behaviour has been observed experimentally for the first time
in nanostructured Manganese. Ultrathin ( 0.6 nm) Manganese nanosheets
have been synthesized inside the two dimensional channels of sol-gel derived
Na-4 mica. The magnetic properties of the confined system are measured within
2K-300K temperature range. The confined structure is found to show a
ferromagnetic behaviour with a nonzero coercivity value. The coercivity value
remains positive throughout the entire temperature range of measurement. The
experimental variation of susceptibility as a function of temperature has been
satisfactorily explained on the basis of a two dimensional system with a
Heisenberg Hamiltonian involving direct exchange interaction.Comment: 13 pages, 9 figure
Magnetodielectric effect of Graphene-PVA Nanocomposites
Graphene-Polyvinyl alcohol (PVA) nanocomposite films with thickness were synthesized by solidification of PVA in a solution with dispersed
graphene nanosheets. Electrical conductivity data were explained as arising due
to hopping of carriers between localized states formed at the graphene-PVA
interface. Dielectric permittivity data as a function of frequency indicated
the occurrence of Debye-type relaxation mechanism. The nanocomposites showed a
magnetodielectric effect with the dielectric constant changing by 1.8% as the
magnetic field was increased to 1 Tesla. The effect was explained as arising
due to Maxwell-Wagner polarization as applied to an inhomogeneous
two-dimensional,two-component composite model. This type of nanocomposite may
be suitable for applications involving nanogenerators.Comment: 13 pages, 11 figure
A model of neutrino mass and dark matter with large neutrinoless double beta decay
We propose a model where neutrino masses are generated at three loop order but neutrinoless double beta decay occurs at one loop. Thus we can have large neutrinoless double beta decay observable in the future experiments even when the neutrino masses are very small. The model receives strong constraints from the neutrino data and lepton flavor violating decays, which substantially reduces the number of free parameters. Our model also opens up the possibility of having several new scalars below the TeV regime, which can be explored at the collider experiments. Additionally, our model also has an unbroken Z2 symmetry which allows us to identify a viable Dark Matter candidate
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