2,697 research outputs found
Fe-spin reorientation in PrFeAsO : Evidences from resistivity and specific heat studies
We report the magnetic field dependence of resistivity () and specific
heat () for the non-superconducting PrFeAsO compound. Our study shows a
hitherto unobserved anomaly at in the resistivity and specific heat
data which arises as a result of the interplay of antiferromagnetic (AFM) Pr
and Fe sublattices. Below the AFM transition temperature (), Pr
moment orders along the crystallographic c axis and its effect on the iron
subsystem causes a reorientation of the ordered inplane Fe moments in a
direction out of the plane. Application of magnetic field introduces
disorder in the AFM Pr sublattice, which, in turn, reduces the out-of-plane
Pr-Fe exchange interaction responsible for Fe spin reorientation. Both in
() and curves, the peak at broadens with the
increase of due to the introduction of the disorder in the AFM Pr
sublattice by magnetic field. In () curve, the peak shifts towards
lower temperature with and disappears above 6 T while in curve
the peak remains visible up to 14 T. The broadening of the anomaly at
in with increasing further confirms that magnetic
field induces disorder in the AFM Pr sublattice.Comment: 8 pages, 10 Figure
Quantm Magnetoresistance of the PrFeAsO oxypnictides
We report the observation of an unusual dependence of transverse
magnetoresistance (MR) in the PrFeAsO, one of the parent compound of pnictide
superconductors. Below the spin density wave transition, MR is large, positive
and increases with decreasing temperature. At low temperatures, MR increases
linearly with up to 14 T. For 40 K, MR vs curve develops a
weak curvature in the low-field region which indicates a crossover from
linear to dependence as 0. The linear MR originates
from the Dirac cone states and has been explained by the quantum mechanical
model proposed by Abrikosov.Comment: accepted for publication in Appl. Phys. Let
Superconductivity in 2-2-3 system Y2Ba2Cu2O(8+delta)
Researchers synthesized a new high T(sub c) 2-2-3 superconductor Y2Ba2Cu3O(8+delta) by a special preparation technique and characterized it by ac-susceptibility measurements. Diamagnetism and Meissner effect sets in at low fields and superconducting transition onsets at 90 K. The systematic investigation of the real and imaginary components of ac-susceptibility as a function of temperature and applied ac magnetic field reveals that the magnetic behavior is that of a granular type superconductor
Scaling of Circulation in Buoyancy Generated Vortices
The temporal evolution of the fluid circulation generated by a buoyancy force
when two-dimensional (2D) arrays of 2D thermals are released into a quiescent
incompressible fluid is studied through the results of numerous lattice
Boltzmann simulations. It is observed that the circulation magnitude grows to a
maximum value in a finite time. When both the maximum circulation and the time
at which it occurs are non-dimensionalised by appropriately defined
characteristic scales, it is shown that two simple Prandtl number (Pr)
dependent scaling relations can be devised that fit these data very well over
nine decades of Pr spanning the viscous and diffusive regimes and six decades
of Rayleigh number (Ra) in the low Ra regime. Also, obtained analytically is
the exact result that circulation magnitude continues to grow in time for a
single buoyant vortex ring in an infinite unbounded fluid.Comment: 4 pages, 3 figures, submitted to Physical Review Letter
Effective interactions and charges in <SUP>58</SUP>Ni
The structure of the low-lying states of 58Ni has been calculated in shell model by assuming an inert 56Ni core plus two valence nucleons in the p3/2, f5/2 and p1/2 orbitals. The two-body matrix elements are first expressed in terms of seven radial matrix elements and these are then parametrized to give best fit between the computed and the observed energies of the levels below 4 MeV. The wave-functions obtained using these two-body matrix elements are used to study the concept of effective charges. It is found that a single effective charge is not sufficient to predict the B(E2) rates equally well for the thirteen known transitions for which experimental values are available. Assumption of state-dependent effective charges gives a far better agreement. An analysis using wave functions obtained with Kuo's two-body matrix elements also gives a similar result
Structure of nuclei in the region A=70
The structure of the selenium nuclei in the region A=70 is studied using our deformed configuration mixing (DCM) shell model based on Hartree-Fock states. An effective interaction given by Kuo and modified by Bhatt is used. An attempt is made to understand the coexistence of shapes in selenium nuclei
Anisotropic magnetic properties and giant magnetocaloric effect in antiferromagnetic MnO crystals (=Dy, Tb, Ho and Yb)
We have systematically investigated the magnetic properties and
magnetocaloric effect (MCE) in MnO (Dy, Tb, Ho and Yb) single
crystals. Above a critical value of applied field (), MnO undergo a
first-order antiferromagnetic (AFM) to ferromagnetic (FM) transition below the
ordering temperature () of moment and a second-order FM to
paramagnetic (PM) transition above . Both and dependence of
shows that the system is highly anisotropic in the FM as well as PM states
and, as a result, the magnetic entropy change () is extremely
sensitive to the direction of applied field and can be negative (normal MCE) or
positive (inverse MCE). For hexagonal HoMnO and YbMnO systems, a very
small inverse MCE is observed only for parallel to c axis and it decreases
with increasing and crosses over to normal one above . On the other
hand, for orthorhombic DyMnO and TbMnO, though the inverse MCE
disappears above along easy-axis of magnetization, it increases rapidly
with along hard-axis of magnetization for . Except for
YbMnO, the values of , relative cooling power and adiabatic
temperature change along easy-axis of magnetization are quite large in the
field-induced FM state for a moderate field strength. The large values of these
parameters, together with negligible hysteresis, suggest that the multiferroic
manganites could be potential materials for magnetic refrigeration in the
low-temperature region.Comment: 10 pages, 11 figure
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