3,232 research outputs found
Bond percolation of polymers
We study bond percolation of non-interacting Gaussian polymers of
segments on a 2D square lattice of size with reflecting boundaries. Through
simulations, we find the fraction of configurations displaying {\em no}
connected cluster which span from one edge to the opposite edge. From this
fraction, we define a critical segment density and the
associated critical fraction of occupied bonds , so that they
can be identified as the percolation threshold in the limit.
Whereas is found to decrease monotonically with for a
wide range of polymer lengths, is non-monotonic. We give
physical arguments for this intriguing behavior in terms of the competing
effects of multiple bond occupancies and polymerization.Comment: 4 pages with 6 figure
Magnetic properties of Hydrogenated Li and Co doped ZnO nanoparticles
The effect of hydrogenation on magnetic properties of Zn0.85Co0.05Li0.10O
nanoparticles is presented. It was found that the sample hydrided at room
temperature (RT) showed weak ferromagnetism (FM) while that hydrided at 400oC
showed robust ferromagnetism at room temperature. In both cases reheating the
sample at 400oC in air converts it back into paramagnetic state (P) completely.
The characterization of samples by X-ray and electron diffraction (ED) showed
that room temperature ferromagnetism observed in the samples hydrogenated at RT
is intrinsic in nature whereas that observed in the samples hydrogenated at
400oC is partly due to the cobalt metal clusters.Comment: 10 pages, 3 figure
Electronic structure of Fe and magnetism in the double perovskites CaFeReO and BaFeReO
The Fe electronic structure and magnetism in (i) monoclinic CaFeReO
with a metal-insulator transition at K and (ii) quasi-cubic
half-metallic BaFeReO ceramic double perovskites are probed by soft
x-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD).
These materials show distinct Fe XAS and XMCD spectra, which are
primarily associated with their different average Fe oxidation states (close to
Fe for CaFeReO and intermediate between Fe and Fe
for BaFeReO) despite being related by an isoelectronic
(Ca/Ba) substitution. For CaFeReO, the powder-averaged Fe
spin moment along the field direction ( T), as probed by the XMCD
experiment, is strongly reduced in comparison with the spontaneous Fe moment
previously obtained by neutron diffraction, consistent with a scenario where
the magnetic moments are constrained to remain within an easy plane. For
T, the unsaturated XMCD signal is reduced below consistent with a
magnetic transition to an easy-axis state that further reduces the
powder-averaged magnetization in the field direction. For BaFeReO, the
field-aligned Fe spins are larger than for CaFeReO ( T) and the
temperature dependence of the Fe magnetic moment is consistent with the
magnetic ordering transition at K. Our results illustrate the
dramatic influence of the specific spin-orbital configuration of Re
electrons on the Fe local magnetism of these Fe/Re double perovskites.Comment: 7 pages, 3 figure
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