V. Ganesan

Publications (51)52.06 Total impact

• Article: Enhancement of the ferromagnetic metallic phase fraction by extrinsic disorder in phase separated La5/8-yPryCa3/8MnO3 (y = 0.45) thin film.

  Dileep K Mishra, V G Sathe, R Rawat, V Ganesan
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  ABSTRACT: Our study shows that extrinsic disorder plays a decisive role in shaping inhomogeneities at large length scales in phase separated systems. Epitaxial La5/8-yPryCa3/8MnO3 (y = 0.45) thin films grown on SrTiO3, LaAlO3 and NdGaO3 substrates exhibited comparable biaxial strain while showing markedly dissimilar extrinsic disorder. Compressively strained film on LaAlO3 is found to be free from extrinsic disorder and has a robust insulating phase with small phase separation while film grown on SrTiO3 shows huge extrinsic disorder due to the strain relaxation process which invokes phase separation at a large length scale that is sufficient to cross the percolation threshold and cause a metal-insulator transition.
  Journal of Physics Condensed Matter 03/2013; 25(17):175003. · 2.55 Impact Factor
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  Available from: S. Shanmukharao Samatham

  Article: Precursor state of skyrmions in MnSi: a heat capacity study

  S Shanmukharao Samatham, V Ganesan
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  ABSTRACT: 1 Introduction In recent times, understanding the various magnetic properties, mainly the so called peculiar "A-phase ", of the chiral magnet MnSi is of great interest. It is observed that the reported magnetic phase diagram is a universal characteristic of all B20 cubic structural com-pounds with non-centrosymmetry and helimagnetic (HM) order [1]. Skyrmion lattice (SkX) is classified as a typical topological excitation. The formation of SkX is reported in thin films of B20 transition metal compounds, Fe 0.5 Co 0.5 Si [2], FeGe [3, 4] where as the precursor states as A-phase are observed in single crystalline Fe 0.8 Co 0.2 Si [5], MnSi [1, 6, 7] and FeGe [8, 9]. Such observation is also reported in thin films as well as bulk form of multiferroic insulating compound Cu 2 OSeO 3 [10, 11]. Amongst these, MnSi stands unique for exhibiting SkX rich phase in all crystal-lographic axes [1]. The various experimental techniques employed are small angle neutron scattering, Lorentz transmission electron microscopy, magnetic susceptibility and Hall resistivity [2, 5, 11–15]. MnSi is a helimagnetic metal that orders at temperature, T < 30 K [16, 17]. Helical spin texture is favoured in MnSi against the ferromagnetic (FM) ordering due to competing interactions like spin exchange and Dzyaloshinskii–Moriya interactions. Skyrmions are themodynamically stable exci-tations and lie in a small window of magnetic field (H) and T. However, a detailed thermodynamic study using heat
  physica status solidi (RRL) - Rapid Research Letters 01/2013; 7(3):184. · 2.22 Impact Factor
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  Available from: S. Shanmukharao Samatham

  Article: Competing localization and quantum interference effects in Fe 0.9 Co 0.1 Si

  S Shanmukharao Samatham, D Venkateshwarlu, Mohan Gangrade, V Ganesan
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  ABSTRACT: Unusual magnetoresistance observed in weak itinerant ferro-magnetic metal Fe 0.9 Co 0.1 Si is addressed. We invoke local-ization effects significantly contributing to the positive magnetoresistance apart from quantum interference effects (QIE), a new mechanism for magnetoresistance at low temper-atures. QIE are dominant only at very low temperatures while localization effects are progressive out of the sub-Kelvin domain. Dominance of localization effects in Kelvin range with increasing applied magnetic field is demonstrated. An uncon-ventional effect of magnetic field on resistivity, favors a least dominant role of ferromagnetic correlations. The H–T phase diagram explore the regions of H 3/2 (paramagnetic region) and QIE (Ds / H 1/2) and its extension into the paramagnetic region. A new region of linear field dependence of MC (Ds / H) is also found and reported. Qualitative analysis of thermopower and its correspondence with electrical resistivity strengthens the concept that the same electrons are responsible for both electrical and magnetic properties. It is also reported that the onset of magnetic and QIE effects is well above T C . 1 Introduction Magnetoresistance (MR) studies are of paramount importance in present-day applications. Soon after the discovery of giant magnetoresistance (GMR) [1], a search for materials exhibiting GMR effect began. GMR has laid the foundations of a new emerging field, namely, spintronics. Intermetallic materials like transition-metal monosilicides have become some of the promising materials suitable for such technological applications [2] with rich physics content [3]. Unravelling the physics behind the unusual properties of materials is always a challenging task. Observation of positive magnetoresistance (PMR) for a ferromagnetic (FM) metal is one such example. For the past few years, attention has been drawn towards understanding the physical proper-ties of doping-driven metal-to-insulator materials. Gener-ally, negative MR is expected for a FM metal since a magnetic field suppresses the scattering from spin fluctu-ations [4]. We will address the unusual PMR observed in Co-doped FeSi, a narrow-gap semiconductor. PMR is observed in materials like antiferromagnetic insulator/metal [5] and the materials that undergo localization effects at low temperatures [6, 7]. Obviously, electron doping to an insulator increases the number of mobile electrons and leads to the finite number of density of states at the Fermi level and hence drives the metallic nature. Aptness of thin films of
  physica status solidi (b) 07/2012; 249(11):2258. · 1.32 Impact Factor
• Article: Structural morphology of amorphous conducting carbon film

  P. N. Vishwakarma, V. Prasad, S. V. Subramanyam, V. Ganesan
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  ABSTRACT: Amorphous conducting carbon films deposited over quartz substrates were analysed using X-ray diffraction and AFM technique. X-ray diffraction data reveal disorder and roughness in the plane of graphene sheet as compared to that of graphite. This roughness increases with decrease in preparation temperature. The AFM data shows surface roughness of carbon films depending on preparation temperatures. The surface roughness increases with decrease in preparation temperature. Also some nucleating islands were seen on the samples prepared at 900°C, which are not present on the films prepared at 700°C. Detailed analysis of these islands reveals distorted graphitic lattice arrangement. So we believe these islands to be nucleating graphitic. Power spectrum density (PSD) analysis of the carbon surface indicates a transition from the nonlinear growth mode to linear surface-diffusion dominated growth mode resulting in a relatively smoother surface as one moves from low preparation temperature to high preparation temperature. The amorphous carbon films deposited over a rough quartz substrate reveal nucleating diamond like structures. The density of these nucleating diamond like structures was found to be independent of substrate temperature (700–900° C).
  Bulletin of Materials Science 04/2012; 28(6):609-615. · 0.88 Impact Factor
• Article: Low temperature thermal windowing (TW) thermally stimulated depolarization current (TSDC) setup

  Deepti Jain, L S Sharath Chandra, R Nath, V Ganesan
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  ABSTRACT: We report here the design and implementation of a precise and easy to operate thermally stimulated depolarization current (TSDC) measurement setup for temperature range 77–400 K. The sample loading is made simple by sandwiching the sample between two copper disk electrodes using a spring-shaft arrangement. The salient features of the setup are precise thermal windowing (TW) capability and linear heating rate over the entire temperature range. The resolution in the measurement of depolarization current is of the order of 7×10−14 A. This is achieved by means of good electrical insulation of the electrodes from the rest of the setup and utilization of low noise circuitry. Precision of the system is demonstrated by its capability to resolve constituent relaxations present in complex relaxation processes using the TW experiments. Study and detection of glass transition processes in polyethylene terephthalate, four relaxation processes in polymethyl methacrylate, glass and crystallization transitions along with the onset of ferroelectric Curie transitions in polyvinylidene fluoride and characterization of electret state in amino acids l-arginine, phenylalanine, tyrosine, tryptophan, glutamic acid, glutamine and methionine show the versatility of our setup.
  Measurement Science and Technology 01/2012; 23(2):025603. · 1.49 Impact Factor
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  Available from: S. Shanmukharao Samatham

  Article: Magnetotransport studies on polycrystalline MnSi

  S Shanmukharao Samatham, D Venkateshwarlu, Mohan Gangrade, V Ganesan
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  ABSTRACT: Correlation of the temperature coefficient of resistivity for doped manganites to the transition temperature, polaron binding energy, and magnetic order Appl. Phys. Lett. 100, 232403 (2012) Carrier localization and out of plane anisotropic magnetoresistance in Nd0.55−xSmxSr0.45MnO3 thin films Appl. Phys. Lett. 100, 222408 (2012) Spin and valley dependent electronic transport in strain engineered graphene
  AIP Conference Proceedings 01/2012; 1447(111):232407-232406.
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  Available from: S. Shanmukharao Samatham

  Article: Transport study on 20% Co doped FeSi in zero field Transport study on 20% Co doped FeSi in zero field Keywords: Magnetic materials, Spin ordering, Transport properties in metal and alloys

  S Shanmukharao Samatham, D Venkateshwarlu, Mohan Gangrade, V Ganesan, Si Ferromagnetic
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  ABSTRACT: We study, experimentally, the zero field temperature dependence of electrical resistance and Seebeck coefficient in B20 cubic type structure Fe metal like to semiconductor like transition temperatures are determined to be 32K and 70K, respectively and electron type charge carriers contributed to the Seebeck coefficient largely and resulted in negative sign. The gradual upturn in thermopower at low temperatures is attributed to change in electronic structure due course of magnetic transition from spin unpolarized to polarized state.
  AIP Conference Proceedings 01/2012; 1447251525(75).
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  Available from: S. Shanmukharao Samatham

  Article: Superconductivity in Cu0.08TiSe2 Superconductivity in Cu 0.08 TiSe 2

  D Venkateshwarlu, S Shanmukharao Samatham, Mohan Gangrade, V Ganesan
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  ABSTRACT: Fluctuation of mean free path and transition temperature induced vortex pinning in (Ba,K)Fe2As2 superconductors Appl. Phys. Lett. 100, 212601 (2012) Transition properties of a YBa2Cu3O7 nanobridge patterned across a twin boundary of a LaAlO3 substrate J. Appl. Phys. 111, 063914 (2012) The influence of the buffer layer architecture on transport properties for BaFe1.8Co0.2As2 films on technical substrates Appl. Phys. Lett. 100, 122602 (2012) Angular dependence of pinning potential, upper critical field, and irreversibility field in underdoped BaFe1.9Co0.1As2 single crystal Abstract. We report here induction of superconductivity by doping Copper (Cu) in the well known CDW conductor, TiSe 2 . Resistivity of parent TiSe 2 and Cu 0.08 TiSe 2 were measured down to 1.8K and fields upto 14T. The CDW transition in the parent compound TiSe 2 is around 150K, as signaled by a huge but broad hump in the resistivity. Upon introduction of Cu in the TiSe 2 matrix, superconductivity is observed. The zero field Tc is 2.92K, is quite interesting and comparable to that of literature. Various superconducting parameters are estimated and discussed.
  AIP Conference Proceedings 01/2012; 8877425(053914).
• Article: Magneto-transport studies of FeSe0.9 − xMx (M = Si, Sb)

  Swati Pandya, Siya Sherif, L S Sharath Chandra, V Ganesan
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  ABSTRACT: We report on the magneto-resistivity of FeSe0.9 − xMx (M = Si, Sb, x = 0.05, 0.1) down to 2 K in the presence of magnetic fields up to 14 T. The superconducting transition shows marginal differences for Sb-and Si-doped samples. Normal state resistivity shows marked changes at intermediate temperatures around 100 K, signaling the presence of a structural transition. It also shows linear behavior with temperature, reminiscent of high Tc ceramics. Superconducting parameters like critical fields and coherence lengths are quantified for all samples. The broadening of superconducting transitions is studied through thermally activated flux flow (TAFF) and fluctuation conductivity. The activation energy of these superconductors is found to be one order smaller than the FeAs-1111 system, which may be explained in terms of larger penetration depth. The activation energy of thermally activated flux flow decreases with the Si and Sb doping and is explained by Kramer's scaling for grain boundary pinning. The zero-field and magnetic-field-induced fluctuation conductivity are studied using Aslamazov–Larkin (AL) and lowest Landau level (LLL) theories, respectively. Zero-field fluctuation conductivity shows the 2D to 3D crossover just above the mean-field transition and 3D LLL scaling is obtained near mean-field transitions for magnetic-field-induced fluctuation conductivity. This is a clear indication of the three-dimensional nature of these superconductors. The 3D nature of these superconductors signifies its potential for future technological applications.
  Superconductor Science and Technology 02/2011; 24(4):045011. · 2.66 Impact Factor
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  Available from: m-hikari.com

  Article: XPS and Raman Studies on (002) Oriented Nanocrystalline ZnO Films Showing Temperature Dependent Optical Red Shift

  K Saravanakumar, C Gopinathan, K Mahalakshmi, V Ganesan, V Sathe, C Sanjeeviraja
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  ABSTRACT: Nanocrystalline zinc oxide (ZnO) thin films have been prepared on glass substrates at different temperatures through planar RF-magnetron sputtering. Structural properties with respect to substrate temperature have been studied with x-ray diffraction (XRD) patterns. The stoichiometry in the films is studied with X-ray photoemission spectroscopy (XPS). The shifts in the absorption edge of the films in the optical spectrum with the variation of substrate temperature are examined. Raman spectrum showed an increase in the average scattering intensity of the phonon peak at 580 cm -1 with respect to the reduction of particle size. The variation of conductivity of prepared ZnO films with respect to substrate temperature is studied well.
  Adv. Studies Theor. Phys. 01/2011; 5:155-170.
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  Available from: S. Shanmukharao Samatham

  Article: Heat Capacity and Magnetocaloric Study on Dy 5 Ge 3 Si

  S Shanmukharao Samatham, Swati Pandya, Mohan Gangrade, L S Sharath, Deepti Jain, V Ganesan
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  ABSTRACT: Here, we report heat capacity and magnetocaloric effect (MCE) on R 5 T 4 ternany compound Dy 5 Ge 3 Si. Heat capacity depicts a peak at 48.4 K which is associated with antiferromagnetic ordering. It gets suppressed and shifts towards low temperatures with field. The estimated critical field is 5T for antiferro to ferromagnetic transition. Heat capacity plays a significant role in determining MCE, where from isothermal entropy change and adiabatic temperature change can be derived. From MCE point of view, sample shows maximum ΔS of 6.6 mJ/g-K at 56.5 K and relative cooling power (RCP) of 356.4 J/kg for temperature range from 46-100 K and hence can be used for magnetic cooling technological applications.
  AIP Conference Proceedings 01/2011; 40.
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  Available from: S. Shanmukharao Samatham

  Article: Large Relative Cooling Power in Dy 5 Si 4 :Dy 5 Si 3 composite

  S Shanmukharao Samatham, Swati Pandya, Mohan Gangrade, L S Sharath, Deepti Jain, V Ganesan
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  ABSTRACT: Anomalously large RCP (Relative Cooling Power) and a reasonable high adiabatic change "ΔT" has been observed in magnetocaloric composite sample Dy 5 Si 4 : Dy 5 Si 3 for a nominal ratio of 2:1. Observed magnetic ordering temperatures for such a composite is 136 K and 39 K respectively which can be assigned to its constituents. Even though the observed "ΔT" is only 5K for a field of 14T, the combined RCP is very large, viz 1283 J/kg. Added merit is the width of temperature over which cooling can be done is 95K. This makes the system more promising and may be a possible candidate for the Ericsson cycle over a temperature range from 140-35K.
  AIP Conference Proceedings 01/2011;
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  Available from: m-hikari.com

  Article: Structural, Optical and Photoconductivity Studies of ZnO: As Nanocrystalline Thin Films

  K Saravanakumar, C Gopinathan, K Mahalakshmi, V Ganesan, V Sathe, C Sanjeeviraja
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  ABSTRACT: Nanocrystalline ZnO:As films prepared using RF-Magnetron sputtering with different substrate temperatures. Structural study has done using x-ray diffraction (XRD) and the lattice parameter is affected to the lattice mismatch of As with Zn and O. we discussed mainly the changes in the optical and steady-state photoconductivity properties of ZnO with the inclusion of As atoms. Further the 102 K. Saravanakumar et al change in the frequency modes are observed with the inclusion of As is identified with Raman Spectrum.
  Contemporary Engineering Sciences. 01/2011; 4:101-117.
• Article: Inspection of multiferroicity in BiMn(2-x)Ti(x)O(5) ceramics through specific heat and Raman spectroscopic studies.

  D K Shukla, Ravi Kumar, S Mollah, R J Choudhary, P N Vishwakarma, V G Sathe, V Ganesan
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  ABSTRACT: Inspection of multiferroicity in BiMn(2 - x)Ti(x)O(5) (0 ≤ x ≤ 0.30) (BMTO) ceramics is performed through specific heat and Raman spectroscopic studies. Thermal variation of specific heat (C) (in the absence and presence of fixed magnetic fields up to 14 T) and Raman spectra of BMTO are presented. In the temperature variation of C, a remarkable anomaly at the antiferromagnetic (AFM) ordering temperature (T(N) ∼ 39 K) is observed in all samples. Pure BiMn(2)O(5) (for x = 0.0) exhibits a larger specific heat anomaly at T(N) compared to that of Ti substituted samples, both in the presence and absence of external magnetic fields. The excess specific heat (ΔC) versus T clearly illustrates appreciable anomalies at ∼ 86 and ∼ 120 K in Ti doped samples related to the magnetic and dielectric transitions, respectively. The low temperature specific heat (LTSH) data indicate a considerably improved ferromagnetic contribution in samples with higher Ti concentration (x > 0.15). The Raman spectra of the doped samples at different fixed temperatures validate the strong electron-phonon coupling corresponding to the observed magnetism and increased harmonicity at dielectric transitions.
  Journal of Physics Condensed Matter 12/2010; 22(48):485901. · 2.55 Impact Factor
• Article: Inspection of multiferroicity in BiMn2 − xTixO5 ceramics through specific heat and Raman spectroscopic studies

  D K Shukla, Ravi Kumar, S Mollah, R J Choudhary, P N Vishwakarma, V G Sathe, V Ganesan
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  ABSTRACT: Inspection of multiferroicity in BiMn2 − xTixO5 (0 ≤ x ≤ 0.30) (BMTO) ceramics is performed through specific heat and Raman spectroscopic studies. Thermal variation of specific heat (C) (in the absence and presence of fixed magnetic fields up to 14 T) and Raman spectra of BMTO are presented. In the temperature variation of C, a remarkable anomaly at the antiferromagnetic (AFM) ordering temperature (TN ~ 39 K) is observed in all samples. Pure BiMn2O5 (for x = 0.0) exhibits a larger specific heat anomaly at TN compared to that of Ti substituted samples, both in the presence and absence of external magnetic fields. The excess specific heat (ΔC) versus T clearly illustrates appreciable anomalies at ~ 86 and ~ 120 K in Ti doped samples related to the magnetic and dielectric transitions, respectively. The low temperature specific heat (LTSH) data indicate a considerably improved ferromagnetic contribution in samples with higher Ti concentration (x > 0.15). The Raman spectra of the doped samples at different fixed temperatures validate the strong electron–phonon coupling corresponding to the observed magnetism and increased harmonicity at dielectric transitions.
  Journal of Physics Condensed Matter 11/2010; 22(48):485901. · 2.55 Impact Factor
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  Available from: Shahid Anwar

  Article: Thermally stimulated depolarization current studies of relaxation in L-asparagine monohydrate

  D. Jain, L.S. Sharath Chandra, S. Bharadwaj, S. Anwar, V. Ganesan, N.P. Lalla, A.M. Awasthi, R. Nath
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  ABSTRACT: Polycrystalline powder samples of L-asparagine monohydrate a fundamental amino acid has been studied for thermal relaxation using Thermally Stimulated Depolarizing Current (TSDC) in its normal and thermal window variations. Blank zero field TSDC, differential scanning calorimetry and x-ray diffraction studies have been performed to explore the effect of heating and cooling cycle on the sample. From the analysis of the results it has been observed that L-asparagine monohydrate undergoes irreversible phase transitions in dehydration and change in crystal structure from orthorhombic for fresh sample to monoclinic for heat-treated sample. Observed depolarization current in case of blank TSDC may be attributed to freezing of the polarization due to structural changes during heating. First TSDC Spectrum of fresh sample has been used for relaxation parameter calculations.
  IEEE Transactions on Dielectrics and Electrical Insulation 09/2010; · 1.09 Impact Factor
• Article: Resistive broadening in sulfur doped FeTe

  Swati Pandya, Siya Sherif, L S Sharath Chandra, V Ganesan
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  ABSTRACT: An analysis of resistive broadening in the presence of magnetic fields up to 14 T for sulfur doped FeTe superconductors is presented. FeTe shows an abrupt change in resistivity at 70 K due to a structural transition. Vanishing of the structural transition and the appearance of superconductivity at ~ 10 K and 9.7 K are seen in FeTe0.9S0.1 and FeTe0.8S0.2 respectively. The upper critical field and coherence lengths are estimated using the Werthamer–Helfand–Hohenberg and Ginzburg–Landau theories for different criteria for the transition temperatures. The estimated activation energy for thermally activated flux flow (TAFF) is an order of magnitude smaller than for the rare earth (R) based RFeAsO1 − xFx system, which indicates weaker pinning than for the RFeAsO1 − xFx system. The flux flow activation energy shows power law behavior with the two different exponents for fields above and below H = 6 T for FeTe0.9S0.1 and H = 8 T for FeTe0.8S0.2. The fluctuation conductivity is analyzed using Aslamazov–Larkin theory and lowest Landau level (LLL) theory, respectively, for zero and nonzero magnetic fields. Incidentally, the field above which 2D LLL scaling is observed in these systems coincides with the crossover field observed in TAFF resistivity.
  Superconductor Science and Technology 06/2010; 23(7):075015. · 2.66 Impact Factor
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  Available from: arxiv.org

  Article: Magnetotransport of La0.70Ca0.3-xSrxMnO3(Ag): A potential room temperature bolometer and magnetic sensor

  V. P. S. Awana, Rahul Tripathi, Neeraj Kumar, H. Kishan, G. L. Bhalla, R. Zeng, L. S. Sharth Chandra, V. Ganesan, H. U. Habermeier
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  ABSTRACT: Here we report the optimized magnetotransport properties of polycrystalline La _0.70 Ca _{0.3- x} Sr _x MnO ₃ and their composites with Ag. The optimization was carried out by varying the Sr and Ag contents simultaneously to achieve large temperature coefficient of resistance (TCR) as well as low field magnetoresistance (MR) at room temperature. Sharpest paramagnetic (PM)-ferromagnetic (FM) and insulator-metal (IM) transition is observed in the vicinity of the room temperature ( T _C≈300 K ≈ T _IM) for the composition La _0.70 Ca _0.20Sr_0.10 MnO ₃: Ag _0.20 . Partial substitution of larger Sr ²⁺ ions at the Ca ²⁺ ions sites controls the magnitude of the FM and IM transition temperatures, while the Ag induces the desired sharpness in these transitions. For the optimized composition, maximum TCR and MR are tuned to room temperature (300 K) with the former being as high as 9% and the later being ∼20 % and ∼30 % at 5 and 10 kOe magnetic fields respectively. Such sharp single peak ( TCR ∼9 % ) at room temperature can be used for the bolometric and infrared detector applications. The achievement of large TCR and low field MR at T ∼300 K in polycrystalline samples is encouraging and we believe that further improvements can be achieved in thin films which by virtue of their low conduction noise are more - - suitable for device applications.
  Journal of Applied Physics 06/2010; · 2.17 Impact Factor
• Article: Enhanced critical parameters of nanocarbon doped MgB2 superconductor

  Monika Mudgel, L. S. Sharath Chandra, V. Ganesan, G. L. Bhalla, H. Kishan, V. P. S. Awana
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  ABSTRACT: The high field magnetization and magnetotransport measurements are carried out to determine the critical superconducting parameters of MgB _2-x C _x system. The synthesized samples are pure phase and the lattice parameter evaluation is carried out using the Rietveld refinement. The R-T(H) measurements are done up to a field of 140 kOe. The upper critical field values, H_c2 , are obtained from these data based on the criterion of 90% of normal resistivity, i.e., H_c2=H at which ρ=90%ρ_N , where ρ_N is the normal resistivity, i.e., resistivity of about 40K in our case. The Werthamer–Helfand–Hohenberg prediction of H_c2(0) underestimates the critical field value even below the field up to which measurement is carried out. After this model, the Ginzburg–Landau theory is applied to the R-T(H) data which not only calculate the H_c2(0) value but also determine the dependence of H_c2 on temperature in the low temperature high field region. The estimated H_c2(0)=157.2 kOe for pure MgB ₂ is profoundly enhanced to 297.5 kOe for the x=0.15 sample in MgB _2-x C _x series. Magnetization measurements are done up to 120 kOe at different temperatures and the other parameters such as irreversibility field H_irr and critical current density J_c(H) are also calculated. The nano carbon doping results in substantial enhancement of critical parameters such as H_c2 , H_irr , and J_c(H) in comparison to the pure MgB ₂ sample.
  Journal of Applied Physics 09/2009; · 2.17 Impact Factor
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  Available from: Sharath Chandra L. S.

  Article: Enhanced Critical parameters of nano-Carbon doped MgB2 Superconductor

  Monika Mudgel, L. S. Sharath Chandra, V. Ganesan, G. L. Bhalla, H. Kishan, V. P. S. Awana
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  ABSTRACT: The high field magnetization and magneto transport measurements are carried out to determine the critical superconducting parameters of MgB2-xCx system. The synthesized samples are pure phase and the lattice parameters evaluation is carried out using the Rietveld refinement. The R-T(H) measurements are done up to a field of 140 kOe. The upper critical field values, Hc2 are obtained from this data based upon the criterion of 90% of normal resistivity i.e. Hc2=H at which Rho=90%Rho; where RhoN is the normal resistivity i.e., resistivity at about 40 K in our case. The Werthamer-Helfand-Hohenberg (WHH) prediction of Hc(0) underestimates the critical field value even below than the field up to which measurement is carried out. After this the model, the Ginzburg Landau theory (GL equation) is applied to the R-T(H) data which not only calculates the Hc2(0) value but also determines the dependence of Hc2 on temperature in the low temperature high field region. The estimated Hc(0)=157.2 kOe for pure MgB2 is profoundly enhanced to 297.5 kOe for the x=0.15 sample in MgB2-xCx series. Magnetization measurements are done up to 120 kOe at different temperatures and the other parameters like irreversibility field, Hirr and critical current density Jc(H) are also calculated. The nano carbon doping results in substantial enhancement of critical parameters like Hc2, Hirr and Jc(H) in comparison to the pure MgB2 sample.
  07/2009;