17,346 research outputs found
Flux jumps, Second Magnetization Peak anomaly and the Peak Effect phenomenon in single crystals of and
We present magnetization measurements in single crystals of the tetragonal
compound, which exhibit the phenomenon of peak effect as well as
the second magnetization peak anomaly for H 0.5T (H c). At the lower
field (50mT H 200mT), we have observed the presence of flux jumps,
which seem to relate to a structural change in the local symmetry of the flux
line lattice (a first order re-orientation transition across a local field in
some parts of the sample, in the range of 100mT to 150mT). These flux jumps are
also observed in a single crystal of for H c in the field
region from 2 mT to 25 mT, which are compatible with the occurrence of a
re-orientation transition at a lower field in a cleaner crystal of this
compound, as compared to those of . Vortex phase diagrams drawn for
H c in and show that the ordered elastic glass
phase spans a larger part of (H, T) space in the former as compared to latter,
thereby, reaffirming the difference in the relative purity of the two samples.Comment: 11 pages, 14 figure
Local electromagnetic properties of magnetic pnictides: A comparative study probed by NMR measurement
75As and 31P NMR studies are performed in PrCoAsO and NdCoPO respectively.
The Knight shift data in PrCoAsO indicate the presence of an antiferromagnetic
interaction between the 4f moments along the c axis in the ferromagnetic state
of Co 3d moments. We propose a possible spin structure in this system. The 75As
quadrupolar coupling constant, increases continuously with the decrease
of temperature and is found to vary linearly with the intrinsic spin
susceptibility, Kiso. This indicates a possibility of the presence of a
coupling between charge density and spin density fluctuations. Further, 31P NMR
Knight shift and spin lattice relaxation rate (1/T1) in the paramagnetic state
of NdCoPO indicate that the differences between LaCoPO and NdCoPO with SmCoPO
are due to the decrement of inter layer separation and not due to the moments
of 4f electrons. Nuclear spin lattice relaxation time (T1) in NdCoPO shows weak
anisotropy at 300 K. Using self consistent renormalization (SCR)theory of
itinerant ferromagnet, it is shown that in the ab plane, the spin fluctuations
are three dimensional ferromagnetic in nature. From SCR theory the important
spin fluctuation parameters (, , ) are evaluated. The
similarities and dissimilarities of the NMR results in As and P based systems,
with different rare earths have also been discussed.Comment: 18 pages,13 figures, accepted for publication in J. Phys. Condens.
Matte
Topological Aspect of high- Superconductivity, Fractional Quantum Hall Effect and Berry Phase
We have analysed here the equivalence of RVB states with FQH states
in terms of the Berry Phase which is associated with the chiral anomaly in 3+1
dimensions. It is observed that the 3-dimensional spinons and holons are
characterised by the non-Abelian Berry phase and these reduce to 1/2 fractional
statistics when the motion is confined to the equatorial planes. The
topological mechanism of superconductivity is analogous to the topological
aspects of fractional quantum Hall effect with .Comment: 12 pages latex fil
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