138 research outputs found
Magnetic Field Induced Coherence-Incoherence Crossover in the Interlayer Conductivity of a Layered Organic Metal
The angle-dependent interlayer magnetoresistance of the layered organic metal
-(BEDT-TTF)KHg(SCN) is found to undergo a dramatic change from
the classical conventional behavior at low magnetic fields to an anomalous one
at high fields. This field-induced crossover and its dependence on the sample
purity and temperature imply the existence of two parallel channels in the
interlayer transport: a classical Boltzmann conductivity and an
incoherent channel . We propose a simple model for
explaining its metallic temperature dependence and low sensitivity to the
inplane field component.Comment: 5 page
Magnetic Transformations in the Organic Conductor kappa-(BETS)2Mn[N(CN)2]3 at the Metal-Insulator Transition
A complex study of magnetic properties including dc magnetization, 1H NMR and
magnetic torque measurements has been performed for the organic conductor
kappa-(BETS)2Mn[N(CN)2]3 which undergoes a metal-insulator transition at
T_MI~25K. NMR and the magnetization data indicate a transition in the manganese
subsystem from paramagnetic to a frozen state at T_MI, which is, however, not a
simple Neel type order. Further, a magnetic field induced transition resembling
a spin flop has been detected in the torque measurements at temperatures below
T_MI. This transition is most likely related to the spins of pi-electrons
localized on the organic molecules BETS and coupled with the manganese 3d spins
via exchange interaction.Comment: 6 pages, 5 Figures, 1 Table; Submitted to Phys.Rev.B (Nov.2010
Staggered Spin Order of Localized pi-electrons in the Insulating State of the Organic Conductor kappa-BETS)2Mn[N(CN)2]3
Magnetic properties of the conduction pi-electron system of
kappa-BETS)2Mn[N(CN)2]3 have been probed using 13C NMR. At ambient pressure,
the metal-insulator transition observed in the resistivity measurements below
T~23K is shown to be accompanied by ordering of the pi-spins in a long-range
staggered structure. As the metal-insulator transition is suppressed by
applying a small pressure of ~0.5 kbar, the pi-spin system maintains the
properties of the metallic state down to 5K.Comment: 13 pages, 4 figure
Angle-dependent magnetoresistance in the weakly incoherent interlayer transport regime
We present comparative studies of the orientation effect of a strong magnetic
field on the interlayer resistance of -(BEDT-TTF)KHg(SCN)
samples characterized by different crystal quality. We find striking
differences in their behavior which is attributed to the breakdown of the
coherent charge transport across the layers in the lower quality sample. In the
latter case, the nonoscillating magnetoresistance background is essentially a
function of only the out-of-plane field component, in contradiction to the
existing theory.Comment: 4 pges, 3 figure
Substitution Effect by Deuterated Donors on Superconductivity in -(BEDT-TTF)Cu[N(CN)]Br
We investigate the superconductivity in the deuterated BEDT-TTF molecular
substitution system
-[(h8-BEDT-TTF)(d8-BEDT-TTF)]Cu[N(CN)]Br, where h8
and d8 denote fully hydrogenated and deuterated molecules, respectively.
Systematic and wide range ( = 0 -- 1) substitution can control chemical
pressure finely near the Mott boundary, which results in the modification of
the superconductivity. After cooling slowly, the increase of
observed up to 0.1 is evidently caused by the chemical pressure
effect. Neither reduction of nor suppression of
superconducting volume fraction is found below 0.5. This demonstrates
that the effect of disorder by substitution is negligible in the present
system. With further increase of , both and superconducting
volume fraction start to decrease toward the values in = 1.Comment: J. Phys. Soc. Jp
Impurity Effect on Superconducting Properties in Molecular Substituted Organic Superconductor -(ET)Cu(NCS)
We report an impurity effect in the organic superconductor
-(ET)Cu(NCS) by substitution of the ET molecule with an
analogue, bis(methyleneditio)tetrathiafulvalene (MT). The superconducting
transition temperature decreases with increasing substitution. The in-plane
magnetic penetration depth is enhanced with substitution, which is
quantitatively attributed to the decrease in the in-plane mean free path. The
enhancement of the penetration depth can also explain the reduction of the
effective pinning in terms of the condensation energy.Comment: 4 pages, submitted to J. Phys. Soc. Jp
Fullerene Black: Relationship between Catalytic Activity in n-alkanes Dehydrocyclization and Reactivity in Oxidation, Bromination and Hydrogenolysis
The reactivity of fullerene black in oxidation (by air oxygen or ions MnO4–or Cr2O7 2– in solution), bromination (by Br2 or (C4H9)4NBr3) and hydrogenolysis (without hydrogenation catalyst) are studied. The dehydrocyclization of n-alkanes over fullerene black is realized via the monofunctional mechanism, i.e. the dehydrogenation and cyclization stages proceed on the same catalytic center. The addition of alumina to the catalyst transforms dehydrocyclization mechanism to bifunctional one, when fullerene black acts as dehydrogenation agent. Reactivity studies and ESR spectroscopy data for initial and annealed fullerene black show the presence in fullerene black structure of both non-conjugated multiple and dangling bonds. Nonconjugated bonds determine catalytic activity and reactivity of fullerene black. They are localized in amorphous part of fullerene black. Technological aspects of fullerene black as alkanes dehydrocyclization catalyst are discussed
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