Shiva Kumar Singh

Bulk Superconductivity in Bismuth Oxysulfide Bi4O4S3

A very recent report on the observation of superconductivity in Bi(4)O(4)S(3) [Mizuguchi, Y.; http://arxiv.org/abs/1207.3145] could potentially reignite the search for superconductivity in a broad range of layered sulfides. We report here the synthesis of Bi(4)O(4)S(3) at 500 °C by a vacuum encapsulation technique and its basic characterizations. The as-synthesized Bi(4)O(4)S(3) was contaminated with small amounts of Bi(2)S(3) and Bi impurities. The majority phase was found to be tetragonal (space group I4/mmm) with lattice parameters a = 3.9697(2) Å and c = 41.3520(1) Å. Both AC and DC magnetization measurements confirmed that Bi(4)O(4)S(3) is a bulk superconductor with a superconducting transition temperature (T(c)) of 4.4 K. Isothermal magnetization (M-H) measurements indicated closed loops with clear signatures of flux pinning and irreversible behavior. The lower critical field (H(c1)) at 2 K for the new superconductor was found to be ~15 Oe. Magnetotransport measurements showed a broadening of the resistivity (ρ) and a decrease in T(c) (ρ = 0) with increasing magnetic field. The extrapolated upper critical field H(c2)(0) was ~31 kOe with a corresponding Ginzburg-Landau coherence length of ~100 Å . In the normal state, the ρ ~ T(2) dependence was not indicated. Hall resistivity data showed a nonlinear magnetic field dependence. Our magnetization and electrical transport measurements substantiate the appearance of bulk superconductivity in as-synthesized Bi(4)O(4)S(3). On the other hand, Bi heat-treated at the same temperature is not superconducting, thus excluding the possibility of impurity-driven superconductivity in the newly discovered superconductor Bi(4)O(4)S(3).

Superconductivity at 5 K in NdO0.5F0.5BiS2

We report appearance of superconductivity at 5 K in NdO0.5F0.5BiS2 and supplement the discovery [Demura et al., e-print arXiv:1207.5248] of the same in layered sulfide based compound. Detailed structural analysis showed that the studied compound is crystallized in tetragonal P4/nmm space group with lattice parameters a = 3.9911(3) A and c = 13.3830(2) A. Bulk superconductivity is established in NdO0.5F0.5BiS2 at 5 K by both transport and magnetic measurements. Electrical transport measurements showed superconducting Tc onset at 5.2 K and Tc (ρ = 0) at 4.7 K. Under applied magnetic field, both Tc onset and Tc (ρ = 0) decrease to lower temperatures and an upper critical field [Hc2(0)] of above 23 kOe is estimated. Isothermal magnetization exhibited typical type-II behavior with lower critical field (Hc1) of around 25 Oe. Specific heat [Cp(T)] is investigated in the temperature range of 1.9–50 K in zero external magnetic field. A Schottky-type anomaly is observed at low temperature below 7 K.

High field (14 T) magneto transport of Sm/PrFeAsO

We report high field magneto transport of Sm/PrFeAsO. Below spin density wave transition (TSDW), the magneto-resistance (MR) of Sm/PrFeAsO is positive and increasing with decreasing temperature. The MR of SmFeAsO is found to be 16%, whereas it is 21.5% in the case of PrFeAsO, at 2.5 K under applied magnetic field of 14 Tesla (T). In the case of SmFeAsO, the variation of isothermal MR with field below 20 K is nonlinear at lower magnetic fields (<2 T) and it is linear at moderately higher magnetic fields (H ≥ 3.5 T). On the other hand, PrFeAsO shows almost linear MR at all temperatures below 20 K. The anomalous behavior of MR being exhibited in PrFeAsO is originated from Dirac cone states. The stronger interplay of Fe and Pr ordered moments is responsible for this distinct behavior. PrFeAsO also shows a hump in resistivity (R-T) with a possible conduction band (FeAs) mediated ordering of Pr moments at around 12 K. However, the same is absent in SmFeAsO even down to 2 K. Our results of high field magneto-tra...

Structural and magnetic properties of Co1−xFexSr2YCu2O7+δ compounds

Here we study the structural and magnetic properties of the Co1−xFexSr2YCu2O7+δ compound (0≤x≤1). X-ray diffraction patterns and simulated data obtained from Rietveld refinement of the same indicate that the iron ion replacement in Co1−xFexSr2YCu2O7+δ induces a change in crystal structure. The orthorhombic Ima2 space group structure of Co-1212 changes to tetragonal P4/mmm with increasing Fe (x≥0.5) ion. The XPS studies reveal that both Co and Fe ions are in mixed states of 3+/4+ for the former and 2+/3+ in case of later. The magnetization with temperature follows Curie–Weiss behavior, in the range of 150–300 K and short magnetic correlations/spin glasslike features below 150 K. The observed magnetic behavior is due to competition of antiferro/ferromagnetic exchange interaction of Co3+ [intermediate spin (IS)]-O–Co3+ (IS)/Co4+ [low spin (LS)] and Fe3+ [high spin (HS)]-O–Fe2+ (LS)/Fe3+ (HS)/Co3+ (IS)/Co4+ (LS) states. Although none of the studied as synthesized samples in Co1−xFexSr2YCu2O7+δ are superconduc...

Superconductivity in the vicinity of ferromagnetism in oxygen free perovskite MgCNi3: An experimental and density functional theory study

We report synthesis, structural, magnetic, specific heat, and density functional theory (DFT) studies on the MgCNi3 superconductor. Polycrystalline MgCNi3 samples are synthesized through the standard solid state reaction route and found to crystallize in the cubic perovskite structure with space group Pm3m, without any detectable trace of Ni impurity. Both AC and DC magnetization exhibited superconducting transition (Tc) at around 7.25 K. The lower critical field (Hc1) and irreversibility field (Hirr) are around 140 Oe and 11 kOe, respectively, at 2 K. The upper critical field (Hc2) being determined from in-field AC susceptibility measurements is 11.6 kOe and 91.70 kOe with 50% and 90% diamagnetism criteria, respectively. Heat capacity (Cp) measurements are carried out under an applied field of up to 140 kOe and down to 2 K. The Sommerfeld constant (γ) and Debye temperature (ΘD) as determined from low temperature fitting of Cp(T) data to the Sommerfeld-Debye model are 36.13 mJ/mol K2 and 263.13 K, respect...

Superconductivity in BiS[sub 2] based Bi[sub 4]O[sub 4]S[sub 3] novel compound

We report here synthesis and basic characterizations of Bi 4 O 4 S 3 superconductor. The sample is crystallized in tetragonal I4/mmm space group with lattice parameters a = 3.969(2) A, c = 41.352(1) A. Both DC magnetization and resistivity measurements confirmed that Bi 4 O 4 S 3 is a bulk superconductor with superconducting transition temperature (Tc ) of 4.4K. Closed loops in isothermal magnetization (MH) measurements are clear signature of flux pinning and irreversible behavior. The lower critical field (Hc1 ) is found to be ∼15 Oe at 2K. The magneto-transport ρ(T, H) measurements showed resistive broadening and decrease in Tc (ρ = 0) with increasing magnetic field. Upper critical field calculated through extrapolation Hc2 (0) is ∼ 31kOe with corresponding Ginzburg-Landau coherence length ∼100 A. Our magnetization and electrical transport measurements substantiate the appearance of bulk superconductivity in as synthesized Bi 4 O 4 S 3 .

Superconductivity in BiS2based Bi4O4S3novel compound

We report here synthesis and basic characterizations of Bi 4 O 4 S 3 superconductor. The sample is crystallized in tetragonal I4/mmm space group with lattice parameters a = 3.969(2) A, c = 41.352(1) A. Both DC magnetization and resistivity measurements confirmed that Bi 4 O 4 S 3 is a bulk superconductor with superconducting transition temperature (Tc ) of 4.4K. Closed loops in isothermal magnetization (MH) measurements are clear signature of flux pinning and irreversible behavior. The lower critical field (Hc1 ) is found to be ∼15 Oe at 2K. The magneto-transport ρ(T, H) measurements showed resistive broadening and decrease in Tc (ρ = 0) with increasing magnetic field. Upper critical field calculated through extrapolation Hc2 (0) is ∼ 31kOe with corresponding Ginzburg-Landau coherence length ∼100 A. Our magnetization and electrical transport measurements substantiate the appearance of bulk superconductivity in as synthesized Bi 4 O 4 S 3 .

Bulk superconductivity at 5K in NdO0.5F0.5BiS2

We report appearance of superconductivity in NdO0.5F0.5BiS2 layered BiS2 sulfide based compound with transition temperature (Tc) 5K (onset). Structural analysis through the X-ray diffraction (XRD) pattern shows that compound is crystallized in tetragonal P4/nmm space group with lattice parameters a = 3.991(3) A, c = 13.383(2) A. Both magnetic and resistivity measurements confirmed bulk superconductivity at 5K. Resistivity behaviour under applied magnetic field shows, both Tc onset and Tc (π = 0) decrease to lower temperatures. The upper critical field [Hc2(0)]∼23kOe is estimated by resistivity measurement.

Superconductivity in BiS2 based Bi4O4S3 novel compound

We report here synthesis and basic characterizations of Bi 4 O 4 S 3 superconductor. The sample is crystallized in tetragonal I4/mmm space group with lattice parameters a = 3.969(2) A, c = 41.352(1) A. Both DC magnetization and resistivity measurements confirmed that Bi 4 O 4 S 3 is a bulk superconductor with superconducting transition temperature (Tc ) of 4.4K. Closed loops in isothermal magnetization (MH) measurements are clear signature of flux pinning and irreversible behavior. The lower critical field (Hc1 ) is found to be ∼15 Oe at 2K. The magneto-transport ρ(T, H) measurements showed resistive broadening and decrease in Tc (ρ = 0) with increasing magnetic field. Upper critical field calculated through extrapolation Hc2 (0) is ∼ 31kOe with corresponding Ginzburg-Landau coherence length ∼100 A. Our magnetization and electrical transport measurements substantiate the appearance of bulk superconductivity in as synthesized Bi 4 O 4 S 3 .