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Ar-Ar age and halogen characteristics of nakhlite MIL 03346: records of crustal processes on Mars
Electrical and Magnetic behaviour of PrFeAsO0.8F0.2 superconductor
The superconducting and ground state samples of PrFeAsO0.8F0.2 and PrFeAsO
have been synthesised via easy and versatile single step solid state reaction
route. X-ray & Reitveld refine parameters of the synthesised samples are in
good agreement to the earlier reported value of the structure. The ground state
of the pristine compound (PrFeAsO) exhibited a metallic like step in
resistivity below 150K followed by another step at 12K. The former is
associated with the spin density wave (SDW) like ordering of Fe spins and later
to the anomalous magnetic ordering for Pr moments. Both the resistivity
anomalies are absent in case of superconducting PrFeAsO0.8F0.2 sample. Detailed
high field (up to 12Tesla) electrical and magnetization measurements are
carried out for superconducting PrFeAsO0.8F0.2 sample. The PrFeAsO0.8F0.2
exhibited superconducting onset (Tconset) at around 47K with Tc({\rho} =0) at
38K. Though the Tconset remains nearly invariant, the Tc({\rho} =0) is
decreased with applied field, and the same is around 23K under applied field of
12Tesla. The upper critical field (Hc2) is estimated from the Ginzburg Landau
equation (GL) fitting, which is found to be ~ 182Tesla. Critical current
density (Jc) being calculated from high field isothermal magnetization (MH)
loops with the help of Beans critical state model, is found to be of the order
of 103 A/cm2. Summarily, the superconductivity characterization of single step
synthesised PrFeAsO0.8F0.2 superconductor is presented.Comment: 15 Pages Text + Fig
Superconductivity and Physical Properties of CaPd2Ge2 Single Crystals
We present the superconducting and normal state properties of CaPd2Ge2 single
crystal investigated by magnetic susceptibility \chi, isothermal magnetization
M, heat capacity C_p, in-plane electrical resistivity \rho and London
penetration depth \lambda versus temperature T and magnetic field H
measurements. Bulk superconductivity is inferred from the \rho(T) and C_p(T)
data. The \rho(T) data exhibit metallic behavior and undergoes a
superconducting transition with T_c onset = 1.98 K and zero resistivity state
at T_c 0 = 1.67 K. The \chi(T) reveal the onset of superconductivity at 2.0 K.
For T>2.0 K, the \chi(T) and M(H) are weakly anisotropic paramagnetic with
\chi_ab > \chi_c. The C_p(T) confirm the bulk superconductivity below T_c =
1.69(3) K. The superconducting state electronic heat capacity is analyzed
within the framework of a single-band \alpha-model of BCS superconductivity and
various normal and superconducting state parameters are estimated. Within the
\alpha-model, the C_p(T) data and the ab plane \lambda(T) data consistently
indicate a moderately anisotropic s-wave gap with \Delta(0)/k_B T_c ~ 1.6,
somewhat smaller than the BCS value of 1.764. The relationship of the heat
capacity jump at T_c and the penetration depth measurement to the anisotropy in
the s-wave gap is discussed.Comment: 12 pages, 9 figures, 2 Tables; Submitted to PR
Large Miscibility Gap in the Ba(Mn_xFe_{1-x})2As2 System
The compounds BaMn2As2 and BaFe2As2 both crystallize in the
body-centered-tetragonal ThCr2Si2-type (122-type) structure at room temperature
but exhibit quite different unit cell volumes and very different magnetic and
electronic transport properties. Evidently reflecting these disparities, we
have discovered a large miscibility gap in the system Ba(Mn_xFe_{1-x})2As2.
Rietveld refinements of powder x-ray diffraction (XRD) measurements on samples
slow-cooled from 1000 C to room temperature (RT) reveal a two-phase mixture of
BaMn2As2 and Ba(Mn_{0.12}Fe_{0.88})2As2 phases together with impurity phases
for x = 0.2, 0.4, 0.5, 0.6 and 0.8. We infer that there exists a miscibility
gap in this system at 300 K with composition limits 0.12 < x < 1. For samples
quenched from 1000 C to 77 K, the refinements of RT XRD data indicate that the
miscibility gap at RT narrows at 1000 C to 0.2 < x < 0.8. Samples with x=0.4,
0.5 and 0.6 quenched from 1100-1400 C to 77 K contain a single 122-type phase
together with significant amounts of Fe_{1-x}Mn_xAs and FeAs2 impurity phases.
These results indicate that the system is not a pseudo-binary system over the
whole composition range and that the 122-type phase has a significant
homogeneity range at these temperatures. Magnetic susceptibility, electrical
resistivity and heat capacity measurements versus temperature of the
single-phase quenched polycrystalline samples with x = 0.2 and 0.8 and for
lightly doped BaMn2As2 crystals are reported.Comment: 14 pages, 16 figures, 3 tables; published versio
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