arXiv subjects

Awadhesh Mani

Publications and source records attributed to Awadhesh Mani.

24 records · Page 2Linked to original sources

arXiv2009

Synthesis, characterization and low temperature studies of iron chalcogenide superconductors

We have synthesized tetragonal iron selenide and telluride superconductors through solid state reaction at 450deg.C and 550deg.C respectively. These synthesis temperatures have been established by optimization. Electrical resistivity and magnetic susceptibility measurements (4.2-300 K) confirm superconductivity with Tc of around 8.5 K in all selenide samples of nominal composition Fe1+deltaSe (delta=0.02-0.22). However, Scanning Electron Microscopy/ Energy Dispersive Spectroscopy studies clearly indicate that the actual stoichiometric ratio of Fe : Se for all the samples synthesized is around 1:1. Also all the samples exhibit identical phase transition temperatures from tetragonal to orthorhombic structure below ~ 100 K implying identical phase composition. The partial substitution of Se by Te leads to an enhancement of Tc to ~ 13 K. The non-superconducting telluride Fe1.09Te exhibits a metal-insulator phase transition at ~ 82 K. Substitution studies of this telluride system by S and Si have in addition been carried out to investigate if chemical pressure induces superconductivity.

cond-mat.supr-con↗

arXiv2009

Superconducting Fe(1+delta)Se(1-x)Te(x) thin films: Growth, characterization and properties

Thin films of Fe(1+delta)Se(1-x)Te(x) (delta ~ 0.18 & x ~ 0.5) have been successfully grown on (100) oriented single crystalline SrTiO3 and LaAlO3 substrates by pulsed laser deposition. The crystal structure was characterized by x-ray diffraction, and the superconducting properties by electrical resistivity measurements. X-ray diffraction analysis establishes the epitaxial growth of the films with c-axis orientation. Atomic force microscopy showed a smooth surface morphology for the films grown on SrTiO3 substrates. All the films are observed to be superconducting with a Tc of ~ 8-14 K depending on the deposition conditions. The deposition parameters were optimized to obtain good quality films with Tc comparable to that of the target material.

cond-mat.supr-con↗

arXiv2009

Pressure induced superconductivity in BaFe2As2 single crystal

The evolution of pressure induced superconductivity in single crystal as well as polycrystalline samples of BaFe2As2 has been investigated through temperature dependent electrical resistivity studies in 0-7 GPa pressure range. While the superconducting transition remains incomplete in polycrystalline sample, a clear pressure induced superconductivity with zero resistivity at the expense of magnetic transition, associated with spin density wave (SDW), is observed in the single crystal sample. The superconducting transition temperature (TC) is seen to increase upto a moderate pressure of about ~1.5 GPa and decreases monotonically beyond this pressure. The SDW transition temperature TSDW decreases rapidly with increasing pressure and vanishes above ~1.5 GPa.

cond-mat.supr-con↗

arXiv2009

Modulation of superconductivity by spin canting in a hybrid antiferromagnet/superconductor oxide

The proximity effect of a C-type antiferromagnet (C-AFM) with the spin canting at low temperature is investigated in the hybrid Nd0.35Sr0.65MnO3(NSCO)/YBa2Cu3O7(YBCO) oxide system through magnetic and transport measurements. It is found that the onset of a spin-canted state destroys partially the superconducting order parameter. Interestingly, due to the instability of this spin-canted state, zero-resistivity recovers at the offset of spin canting. Our result demonstrates clearly the high sensitivity of superconducting order parameter to a modulation of internal field.

cond-mat.supr-con↗

arXiv2005

Effect of Mn substitution on the delicate balance between structure and properties of Gd1.4Ce0.6Sr2RuCu2O10

Some new members of a Ruthenocuprate (2212) series have been synthesized by Mn substitution for Ru in Gd1.4Ce0.6Sr2RuCu2O10 . Characterisation by XRD phase analysis followed by Rietveld refinement has been carried out. IR spectroscopy studies and Rietveld refinements are consistent with substitution of Mn at Ru site. XRD studies indicate changes in structural features on substitution including a significant change in lattice parameter for a very low substitution level (1mole% of Ru). The pristine compound shows coexistence of superconductivity and magnetism. Four probe resistivity studies indicate a semiconductor like upturn in resistivity and absence of superconductivity even for Mn substitution levels as low as 1 mole%. a. c. susceptibility measurements show a progressive suppression of the magnetic transition temperature as well as a smearing of the magnetic transition as a function of Mn substitution. Possible reasons for absence of superconductivity have been discussed.

cond-mat.supr-con↗

arXiv2002

Study of Normal and Superconducting States of MgCNi_3 upon Fe and Co Substitution and External Pressure

Results of our study on the superconducting and normal state properties of the recently discovered superconductor MgCNi_3, the effect of Fe and Co substitution at the Ni site and the effect of pressure are reported. It is shown that a two band model provides a consistent interpretation of the temperature dependence of the normal state resistance and the Hall constant. Whereas band structure calculations suggest an increase in T_c upon partial substitution of Ni with Fe and Co, Co substitution quenches superconductivity and Fe substitution leads to an increase followed by a decrease in T_c. The observed variation of T_c may be explained in terms of a competition between increase in T_c due to increase in density of states and a decrease due to spin fluctuations. Based on these results, it is suggested that the spin fluctuations are weaker in Fe doped samples as compared to the Co doped ones. An initial decrease in T_c (and the normal state resistance) followed by an increase is observed on application of pressure. The decrease in T_c for small applied pressures can be understood in terms of the decrease in the density of states at the Fermi level. The subsequent increase in T_c with pressure is due to a lattice softening or a structural phase transition, consistent with the band structure calculations. It is conjectured that suppression of spin fluctuations by pressure may also be responsible for the observed increase in T_c at higher pressures.

cond-mat.supr-con↗