Neutron Diffraction Studies on La2-xDyxCa2xBa2Cu4+2xOz Superconductors

Structural studies on Dy-substituted La-2125 type superconductors have been carried out by neutron diffraction experiments at room temperature using a monochromatic neutron beam of wavelength lambda = 1.249 Angstroms. A series of samples with La2-xDyxCa2xBa2Cu4+2xOz stoichiometric composition, for x = 0.1 - 0.5, have been studied for their structural properties. A tetragonal Y-123 unit cell was taken as the starting model for the Rietveld analysis. All the samples fit into the starting model, exhibiting no structural transition taking place with increasing dopant concentration. The results of Rietveld analysis and structural properties are discussed in detail

Swift-heavy-ion-irradiation-induced enhancement in electrical conductivity of chemical solution deposited La0.7Ba0.3MnO3 thin films

Epitaxial thin films of La0.7Ba0.3MnO3 manganite, deposited using Chemical Solution Deposition technique, were irradiated by 200 MeV Ag+15 ions with a maximum ion dose up to 1x10^12 ions/cm2. Temperature- and magnetic field-dependent resistivity measurements on all the films (before and after irradiation) reveal a sustained decrease in resistivity with increasing ion dose. A maximum dose of 1x10^12 ions/cm2 suppresses resistivity by factors of 3 and 10, at 330 K [insulator-metal (I-M) transition] and at 10 K, respectively. On the other hand, with increasing ion dose, the magnetoresistance (MR) enhances in the vicinity of I-M transition but decreases at low temperatures. These results, corroborated by surface morphology of films, suggest that the origin of such properties lies in the irradiation induced improved crystallinity and epitaxial orientation, enhanced connectivity between grains, and conglomeration of grains which result in better conductivity at grain boundaries.Comment: To appear in 'Applied Physics Letters

Field-induced abrupt change in magnetization of the manganite compounds (LaR)<SUB>0.45</SUB>(CaSr)<SUB>0.55</SUB>MnO<SUB>3</SUB> (R=Eu and Tb)

The ABO3 type manganites (LaR)0.45(CaSr)0.55MnO3 (R=Eu3+-a nonmagnetic ion and Tb3+-a magnetic ion) which possess large A-site size-disorder, exhibit metamagnetic transitions as a function of magnetic field. Below a certain crossover temperature and depending on the magnetic field sweep rate, the metamagnetic transition transforms from a broad to sharp step-like transitions. This crossover temperature increases on increasing the field sweep rate. The effect of field sweep rate on the critical field of metamagnetic steps decreases with decreasing temperature. This along with the magnetic relaxation and specific heat data provide clear evidence on the contribution of spin-lattice coupling in determining the transformation from smooth to sharp magnetic transitions. These studies also suggest that the A-site magnetism has no important role in transformation from reversible to irreversible magnetization

Structural and superconducting properties of the system La<SUB>1&#8722;x</SUB>PrSr<SUB>x</SUB>CuO<SUB>4</SUB>

Structural and superconducting properties of La<SUB>1&#8722;x</SUB>PrSr<SUB>x</SUB>CuO<SUB>4</SUB> have been investigated. Substitution of Sr for La in LaPrCuO<SUB>4</SUB> (T'-structure), induces a transformation to the T-structure unlike in LaSmCuO<SUB>4</SUB> and LaGdCuO<SUB>4</SUB> where a transformation takes place from the T'- to the T<SUP>&#8727;</SUP>-structure. The transformation gets completed at x=0.2. These studies suggest that the rare earth ionic size is critical in the T' &#8594; T(T<SUP>&#8727;</SUP>) transition. Superconductivity is observed in samples with 0.1 &#8804;&#967;&#8804;0.25

Effect of bandwidth and size disorder on the electrical and magnetotransport properties of doped LaMnO₃ perovskite

324-328Structural, electrical, magnetic and magnetotransport measurements have been carried out on La1-2x PrxCaxMnO3: x =0.20 and 0.30 manganite compounds. These samples form in a distorted orthorhombic structure and behave as nearly low bandwidth systems. Both these samples exhibit insulator-metal transition below 120 K with a large colossal magnetoresistance (CMR) effect at relatively weaker fields (MR=75% at 1 Tesla for x = 0.30 sample).We have also studied the structural, transport and magnetotransport properties of a larger size cation, Sr2+, substituted La0.5Pr0.2Ca0.3-xSrxMnO3(0.0≤x≤0.20) compounds. It is observed that increasing Sr2+ substitution results in an enhancement in transition temperature with a subsequent fall in MR%. The insulator-metal transition temperature for these samples increases from 138 K for x=0.0 to 252 K for x=0.20. The CMR effect fall from 46% for x=0.0 to less than 10% for x=0.20 at a field of 1 Tesla. Also, for samples with higher Sr content the MR% at low temperature is comparable to the MR% in the vicinity of peak resistance. The resistance data in the semiconducting region of all the samples obeys the Mott’s Variable Range Hopping type(lnR  <span style="mso-bidi-font-size:16.0pt;font-family:"Arial Unicode MS","sans-serif"; mso-ansi-language:NL" lang="NL"><img src='http://www.niscair.res.in/jinfo/infinity.gif' border=0> T0.25) of conduction mechanism. </span

Electrical properties of BaTiO3 based – MFIS heterostructure: Role of semiconductor channel carrier concentration

Effect of semiconductor channel carrier concentration on the modifications in the electrical properties of Ag/BaTiO3/SrTiO3/ZnO Metal-Ferroelectric-Insulator-Semiconductor (MFIS) heterostructure has been investigated. Under 4 V applied voltage, low leakage current density ∼3.2 × 10−6 A/cm2, has been observed in ZnO based MFIS heterostructure, which becomes ∼5.0 × 10−6 A/cm2 for MFIS with Al:ZnO channel. Observation of counterclockwise butterfly shaped C-V behavior confirms that, hysteresis in C-V is due to spontaneous ferroelectric polarization and field effect. A device with ZnO semiconductor exhibit ∼2700% modulation which decreases to ∼800% for Al: ZnO channel with good retention behavior. Pulse induced write/erase repeatability of source/drain current confirms the usefulness of the presently studied devices for non-volatile switching memory application

Effect of structural disorder on electrical and magneto transport of La_0.5Pr_0.2R_0.3MnO₃ (R = Sr and Ba) manganite films

354-359The manganite thin films La0.5Pr0.2R0.3MnO3 (R = Sr2+ and Ba2+) have been studied to understand the effect of A-site cationic size disorder (σA2) on their electrical and magneto transport properties. Epitaxial thin films of La0.5Pr0.2Sr0.3MnO3 (LPSMO) and La0.5Pr0.2Ba0.3MnO3 (LPBMO) were synthesized using Pulsed Laser Deposition (PLD) technique with desirable thicknesses of 150 nm. In the present paper, it is shown, how Sr+2 and Ba+2 substitution at La-site leads to half-metallicity in LPSMO and low temperature resistivity minima in LPBMO films, respectively. It is observed that the resistivity and high field magneto resistance (HFMR) increase to ~ 55% in LPSMO and ~ 95% in LPBMO films with increasing size disorder. The increase in cation size disorder in LPBMO as compared to LPSMO, results in high values of positive and negative temperature coefficient of resistance (TCR) ~ 59.8%K−1 and −55.1% K−1, respectively