206 research outputs found
Room-temperature ferromagnetism in nanoparticles of superconducting materials
Nanoparticles of superconducting YBa2Cu3O7-delta (YBCO) (Tc = 91 K) exhibit
ferromagnetism at room temperature while the bulk YBCO, obtained by heating the
nanoparticles at high temperature (940 degree C), shows a linear magnetization
curve. Across the superconducting transition temperature, the magnetization
curve changes from that of a soft ferromagnet to a superconductor. Furthermore,
our experiments reveal that not only nanoparticles of metal oxides but also
metal nitrides such as NbN (Tc = 6 - 12 K) and delta-MoN (Tc ~ 6 K) exhibit
room-temperature ferromagnetism.Comment: 11 pages, 6 figure
Thermal relaxation in charge ordered Pr Ca MnO in presence of a magnetic field
We report observation of substantial thermal relaxation in single crystal of
charge ordered system PrCaMnO in an applied magnetic
field of H = 8T. The relaxation is observed when the temperature is scanned in
presence of a magnetic field in the temperature interval
where is the charge ordering temperature and is charge
melting temperature in a field. In this temperature range the system has
coexisting charged ordered insulator (COI) and ferromagnetic metallic (FMM)
phases. No such relaxation is observed in the COI state in H = 0T or in the FMM
phase at in presence of a magnetic field. We conclude that the
thermal relaxation is due to two coexisting phases with nearly same free
energies but separated by a potential barrier. This barrier makes the
transformation from one phase to the other time-dependent in the scale of the
specific heat experiment and gives rise to the thermal relaxation.Comment: 4 pages LaTEX, 3 eps figure
Optical Limiting in Single-walled Carbon Nanotube Suspensions
Optical limiting behaviour of suspensions of single-walled carbon nanotubes
in water, ethanol and ethylene glycol is reported. Experiments with 532 nm, 15
nsec duration laser pulses show that optical limiting occurs mainly due to
nonlinear scattering. The observed host liquid dependence of optical limiting
in different suspensions suggests that the scattering originates from
microbubbles formed due to absorption-induced heating.Comment: 10 pages, 5 eps figures, to appear in Chem. Phys. Let
Magnetic Field resulting from non-linear electrical transport in single crystals of charge-ordered Pr Ca MnO}
In this letter we report that the current induced destabilization of the
charge ordered (CO) state in a rare-earth manganite gives rise to regions with
ferromagnetic correlation. We did this experiment by measurement of the I-V
curves in single crystal of the CO system
PrCaMnO and simultanously measuring the magnetization
of the current carrying conductor using a high T SQUID working at T = 77K.
We have found that the current induced destabilization of the CO state leads to
a regime of negative differential resistance which leads to a small enhancement
of the magnetization of the sample, indicating ferromagnetically aligned
moments.Comment: 4 pages LateX, 4 eps figure
NO2 and Humidity Sensing Characteristics of Few-layer Graphene
Sensing characteristics of few-layer graphenes for NO2 and humidity have been
investigated with graphene samples prepared by the thermal exfoliation of
graphitic oxide (EG), conversion of nanodiamond (DG) and arc-discharge of
graphite in hydrogen (HG). The sensitivity for NO2 is found to be highest with
DG. Nitrogen-doped HG (n-type) shows increased sensitivity for NO2 compared to
pure HG. The highest sensitivity for humidity is observed with HG. The sensing
characteristics of graphene have been examined for different aliphatic alcohols
and the sensitivity is found to vary with the chain length and branching.Comment: 19 pages, 7 figure
XPS evidence for molecular charge-transfer doping of graphene
By employing x-ray photoelectron spectroscopy (XPS), we have been able to
establish the occurrence of charge-transfer doping in few-layer graphene
covered with electron acceptor (TCNE) and donor (TTF) molecules. We have
performed quantitative estimates of the extent of charge transfer in these
complexes and elucidated the origin of unusual shifts of their Raman G bands
and explained the differences in the dependence of conductivity on n- and
p-doping. The study unravels the cause of the apparent difference between the
charge-transfer doping and electrochemical doping.Comment: 15 pages, 5 figure
Implications and consequences of ferromagnetism universally exhibited by inorganic nanoparticles
Occurrence of surface ferromagnetism in inorganic nanoprticles as a universal
property not only explains many of the unusual magnetic features of oxidic thin
films, but also suggests its possible use in creating new materials, as
exemplified by multiferroic BaTiO3 nanoparticles. While the use of Mn-doped ZnO
and such materials in spintronics appears doubtful, it is possible to have
materials exhibiting coexistence of (bulk) superconductivity with (surface)
ferromagnetism.Comment: 11 pages, 3 figures, 1 tabl
Cooling rate dependence of the antiferromagnetic domain structure of a single crystalline charge ordered manganite
The low temperature phase of single crystals of NdCaMnO
and GdCaMnO manganites is investigated by squid
magnetometry. NdCaMnO undergoes a charge-ordering
transition at =245K, and a long range CE-type antiferromagnetic state
is established at =145K. The dc-magnetization shows a cooling rate
dependence below , associated with a weak spontaneous moment. The
associated excess magnetization is related to uncompensated spins in the
CE-type antiferromagnetic structure, and to the presence in this state of
fully orbital ordered regions separated by orbital domain walls. The observed
cooling rate dependence is interpreted to be a consequence of the rearrangement
of the orbital domain state induced by the large structural changes occurring
upon cooling.Comment: REVTeX4; 7 pages, 4 figures. Revised 2001/12/0
Binding of Nucleobases with Single-Walled Carbon Nanotubes
We have calculated the binding energy of various nucleobases (guanine (G),
adenine (A), thymine (T) and cytosine (C)) with (5,5) single-walled carbon
nanotubes (SWNTs) using ab-initio Hartre-Fock method (HF) together with force
field calculations. The gas phase binding energies follow the sequence G A
T C. We show that main contribution to binding energy comes from
van-der Wall (vdW) interaction between nanotube and nucleobases. We compare
these results with the interaction of nucleobases with graphene. We show that
the binding energy of bases with SWNTs is much lower than the graphene but the
sequence remains same. When we include the effect of solvation energy
(Poisson-Boltzman (PB) solver at HF level), the binding energy follow the
sequence G T A C , which explains the experiment\cite{zheng}
that oligonucleotides made of thymine bases are more effective in dispersing
the SWNT in aqueous solution as compared to poly (A) and poly (C). We also
demonstrate experimentally that there is differential binding affinity of
nucleobases with the single-walled carbon nanotubes (SWNTs) by directly
measuring the binding strength using isothermal titration (micro) calorimetry.
The binding sequence of the nucleobases varies as thymine (T) adenine (A)
cytosine (C), in agreement with our calculation.Comment: 7 pages, 6 figure
Thickness dependence of the stability of the charge-ordered state in PrCaMnO thin films
Thin films of the charge-ordered (CO) compound PrCaMnO
have been deposited onto (100)-oriented SrTiO substrates using the Pulsed
Laser Deposition technique. Magnetization and transport properties are measured
when the thickness of the film is varied. While the thinner films do not
exhibit any temperature induced insulator-metal transition under an applied
magnetic field up to 9T, for thickness larger than 1100\UNICODE{0xc5} a 5T
magnetic field is sufficient to melt the CO state. For this latest film, we
have measured the temperature-field phase diagram. Compared to the bulk
material, it indicates that the robustness of the CO state in thin films is
strongly depending on the strains and the thickness. We proposed an explanation
based on the distortion of the cell of the film.Comment: 9 pages, 6 figures, submitted to Phys. Rev.
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