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    ABSTRACT: Tc(0) increased with increasing CoFe2O4 nanoparticles up to x=1.5.•CoFe2O4 nanoparticles addition has not affected the structure of CuTl-1223.•Addition of CoFe2O4 nanoparticles has improved inter-grains weak links.•Non-monotonic variation of ρ(300 K) (Ω-cm) is due to inhomogeneous distribution of nanoparticles.
    Journal of Magnetism and Magnetic Materials 03/2015; 377. · 2.00 Impact Factor
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    ABSTRACT: The excess conductivity analysis of resistivity versus temperature data of TlBa2(Ca2−yMgy)Cu3O10−δ (y=0.5, 1.0, 1.5) superconductor samples have been performed in the light of Aslamasov-Larkin and Lawrence-Doniach theories before and after irradiation with a beam of gold (Au4+) ions of energy 20 MeV having a fluence of 1×1015 ions/cm2. The microscopic parameters such as zero temperature coherence length {ξc(0)}, inter-plane coupling constant (α), and Fermi velocity (VF) have been calculated from the ln-ln plot of excess conductivity (Δσ) versus reduced temperature (ε) using the Lawrence and Doniach model. The cross-over temperatures separating different fluctuation regions in the ln-ln plot are also determined. It is observed from the excess conductivity analysis that all the microscopic parameters have been decreased after the irradiations. Whereas, calculations have shown that critical magnetic fields (Bc) and critical current density (Jc) are increased after the ion irradiation, which, confirms the validity of the results because Bc and Jc are increased by the formation of artificial pinning centers after bombardment of energetic heavy ion beam.
    Physica B Condensed Matter 01/2015; 457. · 1.28 Impact Factor
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    ABSTRACT: The effects of nano-Alumina (Al2O3) particles inclusion on the structural and superconducting transport properties of (Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ (CuTl-1223) matrix were explored in detail. Different concentrations (i.e. y = 0–1.5 wt.%) of Al2O3 nanoparticles were added to a CuTl-1223 matrix to obtain the desired (Al2O3)y /CuTl-1223 nano-superconducting composites. No significant change was observed in the crystal structure and stoichiometry of the host CuTl-1223 superconducting phase after the addition of Al2O3 nanoparticles. This indicates the occupancy of these nanoparticles at the inter-granular spaces. The superconductivity was suppressed with increasing Al2O3 nanoparticles contents in the CuTl-1223 matrix. The suppression of superconducting properties is most probably due to a pair-breaking mechanism caused by the reflection/scattering of carriers across the insulating nano-Al2O3 particles present at the grain boundaries. The non-monotonic variation of the superconducting properties may be due to inhomogeneous distribution of Al2O3 nanoparticles at the grain boundaries.
    Journal of Electronic Materials 01/2015; 44(1). · 1.64 Impact Factor
  • Journal of Alloys and Compounds 01/2015; 618:110–114. · 2.73 Impact Factor
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    ABSTRACT: Core-shell nickel/nickel-oxide (Ni/NiO) nanoparticles/Cu0.5Tl0.5Ba2Ca2Cu3O10−δ (CuTl-1223) superconductor composites were synthesized by solid-state reaction. The effect of these nanoparticles inclusion on structural and superconducting properties of CuTl-1223 matrix was investigated. Structural, morphological, and compositional properties were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) spectroscopy respectively. Superconducting transport properties were explored by dc-resistivity (ρ) measurements and the different oxygen vibrational modes of the composites were observed by Fourier transforms infrared (FTIR) spectroscopy. The variation of critical temperature (Tc) depends upon the nanoparticles contents in the host superconducting matrix. The overall suppression of Tc with increasing nanoparticles concentration is most probably due to trapping of mobile free carriers and pair-breaking caused by the reflection/scattering of carriers across these nanoparticles having net magnetic moment of metallic nickel in the core of nanoparticles.
    Ceramics International 11/2014; 40(9):13819–13825. · 2.09 Impact Factor
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    K. Nadeem, M. Shahid, M. Mumtaz
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    ABSTRACT: Silica coated (30 wt%) cobalt zinc ferrite (Co1−xZnxFe2O4, x=0, 0.2, 0.3, 0.4, 0.5 and 1) nanoparticles were synthesized by using sol–gel method. Silica acts as a spacer among the nanoparticles to avoid the agglomeration. X-ray diffraction (XRD) reveals the cubic spinel ferrite structure of nanoparticles with crystallite size in the range 37–45 nm. Fourier transform infrared (FTIR) spectroscopy confirmed the formation of spinel ferrite and SiO2. Scanning electron microscopy (SEM) images show that the nanoparticles are nearly spherical and non-agglomerated due to presence of non-magnetic SiO2 surface coating. All these measurements signify that the structural and magnetic properties of Co1−xZnxFe2O4 ferrite nanoparticles strongly depend on Zn concentration and nanoparticle average crystallite size in different Zn concentration regimes.
    Progress in Natural Science 06/2014; · 0.99 Impact Factor
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    ABSTRACT: Low anisotropic (Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ (CuTl-1223) high Tc superconducting matrix was synthesized by solid-state reaction and Al2O3 nanoparticles were prepared separately by co-precipitation method. Al2O3 nanoparticles were added with different concentrations during the final sintering cycle of CuTl-1223 superconducting matrix to get the required (Al2O3)y/CuTl-1223, y = 0.0, 0.5, 0.7, 1.0, and 1.5 wt. %, composites. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy, energy dispersive X-ray, and dc-resistivity (ρ) measurements. The activation energy and superconductivity were suppressed with increasing concentration of Al2O3 nanoparticles in (CuTl-1223) matrix. The XRD analysis showed that the addition of Al2O3 nanoparticles did not affect the crystal structure of the parent CuTl-1223 superconducting phase. The suppression of activation energy and superconducting properties is most probably due to weak flux pinning in the samples. The possible reason of weak flux pinning is reduction of weak links and enhanced inter-grain coupling due to the presence of Al2O3 nanoparticles at the grain boundaries. The presence of Al2O3 nanoparticles at the grain boundaries possibly reduced the number of flux pinning centers, which were present in the form of weak links in the pure CuTl-1223 superconducting matrix. The increase in the values of inter-grain coupling (α) deduced from the fluctuation induced conductivity analysis with the increased concentration of Al2O3 nanoparticles is a theoretical evidence of improved inter-grain coupling.
    Journal of Applied Physics 05/2014; 115(20):203904-203904-6. · 2.21 Impact Factor
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    ABSTRACT: Abstract
    Ceramics International 12/2013; 39(8):9591-9598. · 2.09 Impact Factor
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    ABSTRACT: The effect of irradiations of energetic heavy ion beams on the structural and electrical properties of ZnSe thin films deposited on In2O3:Sn (ITO) coated glass substrate is given. The ZnSe thin films having a thickness of 100 nm were deposited by physical vapour deposition on 200 nm thick ITO coated glass. The ZnSe films were irradiated with 20 MeV carbon, phosphorus and copper ion beams using the 5 MV tandem accelerator at National Centre for Physics, Islamabad. The ion irradiations have shown the improvement in the structural properties in terms of increase in grain size and decrease in the lattice strain. The measurements of photo decay have shown that the decay of the photocurrent has been prolonged in the sample irradiated with carbon ion as compared to the phosphorous and copper irradiated sample.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 10/2013; · 1.19 Impact Factor
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    ABSTRACT: Zinc ferrite (ZnFe2O4)y nanoparticles/Cu0.5Tl0.5Ba2Ca2Cu3O10−δ (CuTl-1223) superconductor composites with y = 0–2 wt.% were prepared by adding ZnFe2O4 nanoparticles into CuTl-1223 superconductor matrix and characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Fourier transforms infrared (FTIR) spectroscopy and dc-resistivity (ρ) measurements. The bulk CuTl-1223 superconductor matrix was synthesized by solid-state reaction and Zinc ferrite (ZnFe2O4) nanoparticles were separately prepared by sol–gel method. XRD analysis revealed the tetragonal and spinel structure of CuTl-1223 superconductor and ZnFe2O4 nanoparticles, respectively. The XRD analysis showed that increased concentration of ZnFe2O4 nanoparticles doesn't disturb the tetragonal structure of host CuTl-1223 superconductor matrix and has no appreciable effect on its lattice parameters. The SEM images confirm the granular structure of the host superconductor matrix. The presence of ZnFe2O4 nanoparticles in host superconductor matrix is confirmed by using FTIR study. Variation of zero resistivity critical temperature {Tc (0)} depends upon the concentration of the nanoparticles in the host superconductor matrix. The overall suppression of Tc (0) and diamagnetism with increasing nanoparticles concentration is most probably due to trapping of mobile free carriers and reflection of spin charge due to presence of paramagnetic ZnFe2O4 nanoparticles. There is possibility for the incorporation of Fe and Zn in the lattice sites during the synthesis process, which may also cause the reduction of Tc (0) of the final composites.
    Solid State Sciences 08/2013; 22:21–26. · 1.67 Impact Factor
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    ABSTRACT: We synthesized (CuO, CaO2, and BaO)y/Cu0.5Tl0.5Ba2Ca2Cu3O10−δ (y = 0, 5%, 10%, 15%) composites by solid-state reaction and characterized them by x-ray diffraction, scanning electron microscopy, dc-resistivity, and Fourier transform infrared spectroscopy. Frequency and temperature dependent dielectric properties, such as real and imaginary parts of the dielectric constant, dielectric loss, and ac-conductivity of these composites were studied by capacitance and conductance measurements as a function of frequency (10 kHz to 10 MHz) and temperature (78 to 300 K). X-ray diffraction analysis reveals that the characteristic behavior of the superconductor phase and the structure of Cu0.5Tl0.5Ba2Ca2Cu3O10−δ are nearly undisturbed by doping with nanoparticles. Scanning electron microscopy images show the improvement in the intergranular linking between the superconducting grains occurring with increasing nanoparticle concentration. Microcracks are healed up with these nanoparticles, and superconducting volume fraction is also increased. Dielectric properties of these composites strongly depend on the frequency and temperature. Zero resistivity critical temperature and dielectric properties show opposite trends with the addition of nanoparticles to the Cu0.5Tl0.5Ba2Ca2Cu3O10−δ superconductor matrix.
    Low Temperature Physics 07/2013; 39(7). · 0.82 Impact Factor
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    ABSTRACT: The temperature and frequency dependent dielectric properties of polycrystalline Cd-doped Cu0.5Tl0.5Ba2Ca3(Cu4−y Cdy )O12−δ (y=0,0.25,0.5,0.75) bulk superconductor samples are investigated. The zero resistivity critical temperature {T c(R=0)} has decreased and normal state resistivity has increased with the increase of Cd-doping in Cu0.5Tl0.5Ba2Ca3(Cu4−y Cdy )O12−δ samples. The dielectric properties such as dielectric constants (ε′,ε″), dielectric loss tangent (tanδ) and ac-conductivity (σ ac ) are investigated by measuring the capacitance (C) and conductance (G) in the frequency range of 10 KHz to 10 MHz at different temperature from 80 K to 300 K. The negative capacitance (NC) is observed in all Cu0.5Tl0.5Ba2Ca3(Cu4−y Cdy )O12−δ samples. The large values of NC observed at lower frequencies and temperatures may be due to reduced thermal vibrations and enhanced polarizability of the material. The effect of Cd-doping on bulk properties, dc-resistivity (ρ) and ac-electrical conductivity (σ ac ) of these superconductor samples are investigated. The polarization in Cu0.5Tl0.5Ba2Ca3(Cu4−y Cdy )O12−δ samples is most likely arising from the displacement of charges in CuO2/CdO2 planes relative to the static charges at Ba2+, Tl3+, and Cu2+ sites in Cu0.5Tl0.5Ba2O4−δ charge reservoir layers by external applied field.
    Journal of Low Temperature Physics 01/2013; 172(1-2). · 1.18 Impact Factor
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    ABSTRACT: Synthesis and characterization of (CuO)x /Cu0.5Tl0.5Ba2Ca2Cu3O10−δ ; {(CuO)x /CuTl-1223} composites with x=0 %, 10 %, 15 % and 20 % have been reported. The fluctuations induced conductivity (FIC) analysis of (CuO)x /CuTl-1223 composite has been carried out using Aslamazov-Larkin (AL) and Lawrence-Doniach (LD) models in the temperature regime well above the critical temperature (T>T c ). The electrical resistivity versus temperature curves of as-prepared and oxygen post-annealed (CuO)x /CuTl-1223 composite were fitted by using above mentioned models to extract the microscopic parameters such as zero temperature coherence length along c-axis{ξ c (0)}, inter-layer coupling (J), dimensional critical exponent (λ) and inter-grain coupling constant (α) etc. It has been observed that the cross-over temperature (T o ) fits very well the two-dimensional (2D) and three-dimensional (3D) AL equations and shifts towards the lower temperature regime with the enhanced weight percentage of CuO nano-particles. The shifting of AL 3D region to higher temperature after oxygen post-annealing indicates the restoration of oxygen and optimization of charge carriers in conducting CuO2 planes. The gradual decrease in the value of inter-grain coupling constant (α) with the increase of CuO nano-particles content reflects an improvement in the inter-grain coupling resulting into an increase in the coherence length (ξ c ) along the c-axis. Almost all superconductivity parameters have been improved after oxygen post-annealing. The suppression of superconductivity parameters in the composite with x=20 % limits the optimum doping level of CuO nano-particles in (CuO)x /CuTl-1223 composite.
    Journal of Low Temperature Physics 01/2013; 170(3-4):185-204. · 1.18 Impact Factor
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    M Mumtaz, Nawazish A Khan
    Ceramics International. 01/2013;
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    Applied Superconductivity, IEEE Transactions on. 01/2013; 23(2):8800108-8800108.
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    ABSTRACT: The superconducting properties of Zn-doped Cu0.5Tl0.5Ba2Ca2(Cu3−yZny)O10−δ {CuTlZn-1223} (y=0, 0.83, 1.66, 2.5) samples prepared at 820, 830, 850 and 860 °C have been compared. The samples were investigated by x-ray diffraction (XRD), dc-resistivity, ac-susceptibility and Fourier Transform Infrared (FTIR) absorption measurements. Almost all the superconducting properties have been increased to their maximum in all CuTlZn-1223 samples synthesized at 860 °C, which shows that 860 °C is the optimum temperature to achieve CuTlZn-1223 with enhanced superconducting properties.
    Ceramics International. 12/2012; 38(8):6417–6422.
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    ABSTRACT: We have doped Zn at the Cu planar sites in Cu0.5Tl0.5Ba2Ca3Cu4−yZnyO12−δ (y = 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0) superconductors, which decrease the population of small spins of Cu atoms and most likely suppress the anti-ferromagnetically aligned spins in the inner-CuO2 planes (IP). For the observation of such effects, fluctuation induced conductivity (FIC) analyses of the above mentioned samples have been carried out using the Aslamazov–Larkin (AL) theory in the critical regime closer to the transition temperature (Tc) and the Lawrence–Doniach (LD) model closer to Tc and above. The idea behind these analyses is the fact that Cooper pair formation starts well above Tc. The influence of the Cooper-pairs on the normal electrons is determined by the Maki-Thompson (MT) model. From these analyses we have determined the coherence length along the c-axis (ξc(0)), the inter-plane coupling constant (J), the phase relaxation time of the carriers (τφ), the Fermi velocity (VF) of the carriers and the energy required to break apart the electrons pairs (Epb). Using the Ginzburg number (NG) and the Ginzburg–Landau (GL) equations, the thermodynamic critical magnetic field (Bc(0)), the lower critical field (Bc1(0)), the upper critical field (Bc2(0)), the critical current density (Jc(0)) and the penetration depth (λp.d) are also calculated. Four fluctuation regions above Tc are observed for all of the samples, namely the critical (cr), three dimensional (3D), two dimensional (2D) and zero dimensional (0D) fluctuation regions. The values of Bc(0), Bc1(0) and Jc(0) are increased while the values of E and λp.d are suppressed with increasing Zn content at Cu sites. The intersection of 2D LD, and 0D exponents determines a cross-over of 2D LD & MT contributions. Associated with the width of 3D AL/LD regimes, the crossover temperature T3D-2D is shifted to higher values with enhanced Zn doping. It is most likely that decreased density of small spins of Cu atoms induced by increased Zn doping, may suppress the spin scatterings that consequently result in higher values of T3D-2D, critical fields (Bc(0), Bc1(0)), Jc(0) and lower values of Epb and λp.d in the final compound. The decreased density of small spins of Cu atoms in the CuO2/ZnO2 planes is viewed in terms of suppression of the spin gap and, hence, the pseudo-gap in Cu0.5Tl0.5Ba2Ca3Cu4−yZnyO12−δ (y = 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0) superconductors.
    Physica C Superconductivity 08/2012; 478:32–37. · 0.72 Impact Factor
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    ABSTRACT: The fluctuation induced conductivity (FIC) analysis of (Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ superconductor synthesized at different temperatures has been carried out in the frame work of Aslamazov-Larkin (AL) theory. Almost all the superconducting parameters studied in this research work have been improved with the increase of synthesis temperature up to 850°C, which is most likely due to (Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ superconducting phase stability at this synthesis temperature. The parameters calculated from FIC analysis are cross-over temperature (T 0), zero temperature c-axis coherence lengths ξ c (0), interlayer coupling strength (J) and the exponents (λ 3D and λ 2D). The FIC analysis has shown an increase in T 0 and the shift of three dimensional (3D) Aslamazov-Larkin (AL) regions to the higher temperature with the increase in synthesis temperature up to 850°C.
    Journal of Low Temperature Physics 01/2012; 167(1-2):74-82. · 1.18 Impact Factor
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    ABSTRACT: The superconductivity parameters of (Cu1−x Tlx )Ba2Ca4Cu5O14−δ (CuTl-1245) samples synthesized at different temperatures has been compared. Almost all the superconductivity parameters studied in this research work are suppressed with the increase of synthesis temperature beyond 890 ○C, which may be due to defects induced by the volatility of some constituents such as thallium, oxygen deficiencies, and multiphase in the final compound. The fluctuation induced conductivity (FIC) analysis has shown a decrease in the cross-over temperature (T o) as well as the mean-field critical temperature ( $T_{\mathrm{c}}^{\mathrm{mf}})$ and the shift of three- dimensional (3D) Aslamasov–Larkin (AL) regions to the lower temperature with the increase of synthesis temperature beyond 890 ○C. A direct correlation between (T o), the zero temperature coherence length {ξ c (0)}, the interlayer coupling strength (J), mean-field critical temperature ( $T_{\mathrm{c}}^{\mathrm{mf}})$ as well as carrier concentration has also been observed.
    Journal of Superconductivity and Novel Magnetism 01/2012; 25(2):325-329. · 0.93 Impact Factor

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