170 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
Anomalous thermal expansion of SbTe topological insulator
We have investigated the temperature dependence of the linear thermal
expansion along the hexagonal c axis (), in-plane resistivity
(), and specific heat () of the topological insulator SbTe
single crystal. exhibits a clear anomaly in the temperature region
204-236 K. The coefficient of linear thermal expansion decreases
rapidly above 204 K, passes through a deep minimum at around 225 K and then
increases abruptly in the region 225-236 K. is negative in the
interval 221-228 K. The temperature dependence of both and can
be described well by the Debye model from 2 to 290 K, excluding the region
around the anomaly in
Adsorption Characteristics of Congo Red Dye onto PAC and GAC based on S/N ratio:A Taguchi Approach
Adsorption characteristics of Congo Red dye(CR)on powdered activated carbon(PAC)and granular activated carbon(GAC)from aqueous solutions was studied. The potential for the adsorption of Congo Red dye at a fixed initial concentration of 100 ppm on PAC and GAC was carried out. The experiments were carried out in a batch system to optimize operation variables :pH,time and temperature for the same adsorbent dosage of 0.2 mg in 50ml of dye solution.The Taguchi experimental design method was applied for the systematic and effective investigation of the optimal conditions of operation variables.The pH of the solution remains the major influencing factor for the adsorption process in all the experimental runs
The magnetization of PrFeAsOF$_{0.12} sueprconductor
The magnetization of the PrFeAsOF polycrystalline sample
has been measured as functions of temperature and magnetic field . The
observed total magnetization is the sum of a superconducting irreversible
magnetization () and a paramagnetic magnetization (). Analysis of dc
susceptibility in the normal state shows that the paramagnetic
component of magnetization comes from the Pr magnetic moments. The
intragrain critical current density derived from the magnetization
measurement is large. The curve displays a second peak which shifts
towards the high-field region with decreasing temperature. In the low-field
region, a plateau up to a field followed by a power law
behavior of is the characteristic of the strong pinning. A vortex
phase diagram for the present superconductor has been obtained from the
magnetization and resistivity data.Comment: A revised version with modified title,8 pages, 7 figure
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Tuning the interplay between nematicity and spin fluctuations in Na1-x Li x FeAs superconductors
Strong interplay of spin and charge/orbital degrees of freedom is the fundamental characteristic of the iron-based superconductors (FeSCs), which leads to the emergence of a nematic state as a rule in the vicinity of the antiferromagnetic state. Despite intense debate for many years, however, whether nematicity is driven by spin or orbital fluctuations remains unsettled. Here, by use of transport, magnetization, and 75As nuclear magnetic resonance (NMR) measurements, we show a striking transformation of the relationship between nematicity and spin fluctuations (SFs) in Na1-x Li x FeAs; For x ≤ 0.02, the nematic transition promotes SFs. In contrast, for x ≥ 0.03, the system undergoes a non-magnetic phase transition at a temperature T 0 into a distinct nematic state that suppresses SFs. Such a drastic change of the spin fluctuation spectrum associated with nematicity by small doping is highly unusual, and provides insights into the origin and nature of nematicity in FeSCs
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