99 research outputs found
Oxygen non-stoichiometry in Ru-1212 and Ru-1222 magnetosuperconductors
Here we report the results of thermogravimetric (TG) analysis on the oxygen
non-stoichiometry of RuSr2GdCu2O8 (Ru-1212) and
RuSr2(Gd0.75Ce0.25)2Cu2O10(Ru-1222) samples. With TG annealings carried out in
O2 and Ar atmospheres it was found that the oxygen content in Ru-1212 remains
less affected upon various annealings, while for Ru-1222 wider-range
oxygen-content tuning is possible. When heated in H2/Ar atmosphere the both
phases release oxygen upon breaking down to mixtures of metals (Ru and Cu) and
binary oxides (CeO2, Gd2O3, and SrO) in two distinct steps around 300 and 450
oC. This reductive decomposition reaction carried out in a thermobalance was
utilized in precise oxygen content determination for these phases. It was found
that the 100-atm O2-annealed Ru-1212 sample was nearly stoichiometric, while
the similarly treated Ru-1222 sample was clearly oxygen deficient. X-ray
absorption near-edge (XANES) spectroscopy was applied to estimate the valence
of Ru in the samples. In spite of the fact that the Ru-1212 phase was shown to
possess less oxygen-deficient RuO2 layer, the valence of Ru as probed with
XANES was found to be lower in Ru-1212 than that in Ru-1222.Comment: 11 pages text, 4 pages Figs. To ISS 2002 YOKOHAMA for PHYSICA
Magneto-superconductivity of 100-atm O2-annealed RuSr2Gd1.5Ce0.5Cu2O10
Studied 100-atm O2-annealed RuSr2Gd1.5Ce0.5Cu2O10 (Ru-1222) compound
crystallized in a tetragonal I4/mmm space group crystal structure.
Thermo-gravemetric (TG) analysis of the compound showed the release of oxygen
and breaking to metallic constituents in two distinct steps at around 350 and
500 0C. The DC magnetization data (M vs. T) revealed magnetic transition at 100
K followed by superconducting transition at 40 K. Low field M vs. H hysteresis
loop showed a lower critical field (Hc1) value of around 25 Oe. Ferromagnetic
component is evidenced at 5, 10, 20 and 40 K. Near saturation field of above 5
Tesla is observed at 5 K. Zero-field returning moment (Mr) and zero-moment
coercive field (Hc) values at 5 K are 0.35mB and 250 Oe. The resistance vs.
temperature (R vs. T) behaviour of the sample confirmed superconductivity at
around 43 K. Superconductivity transition (Tc) is broadened under magnetic
field with strong granularity like steps.Comment: 16 pages including text and six figure
Appearance and disappearance of superconductivity in SmFe1-xNixAsO (x = 0.0 to 1.0)
Bulk polycrystalline Ni-substituted SmFe1-xNixAsO (x = 0.0 to 1.0) samples
are synthesized by solid state reaction route in an evacuated sealed quartz
tube. The cell volume decreases with increase of Ni content in SmFe1-xNixAsO,
thus indicating successful substitution of smaller ion Ni at Fe site. The
resistivity measurements showed that the spin-density-wave (SDW) transition is
suppressed drastically with Ni doping and subsequently superconductivity is
achieved in a narrow range of x from 0.04 to 0.10 with maximum Tc of 9K at x =
0.06. For higher content of Ni (x > 0.10), the system becomes metallic and
superconductivity is not observed down to 2K. The magneto-transport [R(T)H]
measurements exhibited the upper critical field [Hc2(0)] of up to 300kOe. The
flux flow activation energy (U/kB) is estimated ~98.37K for 0.1T field.
Magnetic susceptibility measurements also confirms bulk superconductivity for x
= 0.04, 0.06 and 0.08 samples. The lower critical field (Hc1) is around 100Oe
at 2K for x = 0.06 sample. Heat capacity CP(T) measurements exhibited a hump
like transition pertaining to SDW in Fe planes at around 150K and an AFM
ordering of Sm spins below temperature of 5.4K for ordered Sm spins [TN(Sm)].
Though, the SDW hump for Fe spins disappears for Ni doped samples, the TN (Sm)
remains unaltered but with a reduced transition height, i.e., decreased
entropy. In conclusion, complete phase diagram of SmFe1-xNixAsO (x = 0.0 to
1.0) is studied in terms of its structural, electrical, magnetic and thermal
properties.Comment: 18 pages text + Figures; comments suggestions welcome
([email protected]
Room temperature magnetic entropy change and magnetoresistance in La_{0.70}(Ca_{0.30-x}Sr_x)MnO_3:Ag 10% (x = 0.0-0.10)
The magnetic and magnetocaloric properties of polycrystalline
La0.70(Ca0.30-xSrx)MnO3:Ag 10% manganite have been investigated. All the
compositions are crystallized in single phase orthorhombic Pbnm space group.
Both, the Insulator-Metal transition temperature (TIM) and Curie temperature
(Tc) are observed at 298 K for x = 0.10 composition. Though both TIM and Tc are
nearly unchanged with Ag addition, the MR is slightly improved. The MR at 300 K
is found to be as large as 31% with magnetic field change of 1Tesla, whereas it
reaches up to 49% at magnetic field of 3Tesla for La0.70Ca0.20Sr0.10MnO3:Ag0.10
sample. The maximum entropy change (\DeltaSMmax) is 7.6 J.Kg-1.K-1 upon the
magnetic field change of 5Tesla, near its Tc (300.5 K). The
La0.70Ca0.20Sr0.10MnO3:Ag0.10 sample having good MR (31%1Tesla, 49%3Tesla) and
reasonable change in magnetic entropy (7.6 J.Kg-1.K-1, 5 Tesla) at 300 K can be
a potential magnetic refrigerant material at ambient temperatures.Comment: 11 pages text + Figs comments/suggestions
([email protected]
Crystal growth and magneto-transport of Bi2Se3 single crystals
In this letter, we report on the growth and characterization of bulk Bi2Se3 single crystals. The studied Bi2Se3 crystals are grown by the self-flux method through the solid-state reaction from high-temperature (950 °C) melt
of constituent elements and slow cooling (2 °C/h). The resultant crystals are shiny and grown in the [00l] direction, as evidenced from surface XRD. Detailed Reitveld analysis of powder X-ray diffraction (PXRD) of the crystals
showed that these are crystallized in the rhombohedral crystal structure with a space group of R3m (D5), and the lattice parameters are a = 4.14 (2), b = 4.14 (2), and c = 28.7010 (7) A° . Temperature versus resistivity (ρ − T ) plots revealed metallic conduction down to 2 K, with typical room temperature resistivity (ρ300 K) of around 0.53 mΩ-
cm and residual resistivity (ρ0 K) of 0.12 mΩ-cm. Resistivity under magnetic field [ρ(T )H] measurements exhibited large+ve magneto-resistance right from 2 to 200 K. Isothermal
magneto-resistance [ρH] measurements at 2, 100, and 200 K exhibited magneto-resistance (MR) of up to 240 %, 130 %, and 60 %, respectively, at 14 T. Further, the MR plots are nonsaturating and linear with the field at all temperatures. At 2 K, the MR plots showed clear quantum oscillations at above say 10 T applied field. Also, the Kohler plots, i.e., Δρ/ρo versus B/ρ, were seen consolidating on one plot. Interestingly, the studied Bi2Se3 single crystal exhibited the Shubnikov-de Haas (SdH) oscillations at 2 K under different applied magnetic fields ranging from 4 to 14 T
Anomalous lattice expansion of RuSr2Eu1.5Ce0.5Cu2O10(Ru-1222) magneto superconductor: A low temperature X-ray diffraction study
This is the first report of the observation of the onset of excess volume and
also of the strain along the a-axis near the magnetic ordering temperature in
Ru-1222 superconductor, and indicates a coupling between the lattice and the
magnetism in this system. Magnetization, magneto transport and thermoelectric
power measurements being carried out on the same sample are also reported.Comment: 15 Pages Text Plus Figs. Physica C (2006) accepte
Appearance of superconductivity in new BiS2 based layered LaO0.5F0.5BiS2
We report here synthesis, structural, DC magnetization, and transport studies
of new BiS2 based layered LaO0.5F0.5BiS2 superconductor [1]. The sample was
synthesized by conventional solid state route via vacuum encapsulation
technique at 800oC for 12h. LaO0.5F0.5BiS2 crystallizes in tetragonal P4/nmm
space group with lattice parameters a = 4.0703(5){\AA}, c = 13.3902(4){\AA}.
Bulk superconductivity is confirmed with superconducting transition temperature
(Tc) of 2.7K by DC magnetization measurements. The Isothermal magnetization
(MH) measurements showed closed loops with clear signatures of flux pinning and
irreversible behavior. The resistivity measurements confirmed an onset Tc of
2.7K. The magneto-transport {\rho}(T,H) measurements showed a resistive
broadening and decrease in Tc ({\rho}=0) to lower temperatures with increasing
magnetic field. The magnetic phase diagram involving upper critical and
irreversibility fields as a function of temperature has been ascertained. Our
DC magnetization and electrical transport measurements confirm the appearance
of bulk superconductivity in LaO0.5F0.5BiS2 superconductor.Comment: 11 pages figures + Text: First observation/approval of LaO/FBiS2
superconductivity: comments/suggestions: [email protected]
Micro-structure and Magnetization of the 80-K Superconductor, TbSr2Cu2.7Mo0.3O7+d
The results of micro-structural and detailed magnetization studies are
reported here for our recently published TbSr2Cu2.7Mo0.3O7+d superconductor
with a transition temperature (Tc) at as high as 80 K [1]. From XRD and EDX the
sample was confirmed to be of single-phase and possess the nominal cation
stoichiometry. The SEM images showed well-developed grains for this ceramic
high-Tc superconductor. Magnetization measurements at various temperatures and
fields revealed bulk superconductivity below 80 K. Magnetization versus applied
field (M vs. H) loops at various temperatures below the Tc exhibited clear full
penetration field HP. In normal state (> 100 K) the susceptibility follows the
Curie-Weiss behavior with an effective paramagnetic moment of 9.83 mB.Comment: 11 pages of text and figs. Accepted in Physica
Role of interstitial "caged" Fe in the superconductivity of FeTe1/2Se1/2
All samples are synthesized through standard solid state reaction route and
are quenched to room temperature systematically at 7000C, 5000C, 3000C and room
temperature (RT); named as 700Q, 500Q, 300Q and RTQ respectively. The
structural and magnetic properties are studied. Careful Reitveld analysis of
XRD patterns revealed that though all samples except 700Q are crystallized in
single phase with space group P4/nmm, the presence of interstitial Fe (Feint)
at 2c site is increased from 5% for RTQ to 8% for 500Q. The 700Q sample is
crystallized in Fe7Se8 phase. The transport and magnetization results revealed
that though RTQ and 300Q are superconducting at 10 K and 13 K respectively,
while the 500Q and 700Q are not. Magnetic ordering (Tmag) is observed at around
125 K for all the samples. The prominence of Tmag in terms of effective moment
is sufficiently higher for 500Q and 700Q than RTQ and 300Q. Summarily it is
found that quenching induced disorder affects the occupancy of interstitial Fe
in FeTe1/2Se1/2 and thus both its superconducting and magnetic properties.
Further it clear that limited presence of interstitial Fe at 2c site is not
fully against observation of superconductivity, because 300Q sample possesses
higher Tc (13 K) for higher Feint (6%) than RTQ sample with relatively lower Tc
(10 K) having lower Feint (5%). Further the 500Q sample with much higher Feint
(8%) is though non-superconducting.Comment: 8 pages text + figures contact- [email protected]
- …