D. G. Kuberkar

Magnetic and transport properties of (La0.7−2xEux)(Ca0.3Srx)MnO3: Effect of simultaneous size disorder and carrier density

Structural, magnetic and transport studies have been carried out on (La0.7−2xEux)(Ca0.3Srx)MnO3 (0.05⩽x⩽0.25) compounds forming in a distorted orthorhombic structure (space group Pnma, No. 62). The Eu and Sr substitutions avoid any average A-site cation size disparity throughout the series. However, increasing both the cation size mismatch at the A-site and carrier concentration induces interesting changes in structural, transport and magnetic properties. Both insulator–metal transition temperature (Tp) and Curie temperature (TC) decrease with increasing x. The resistivity of all the samples in the semiconducting regime fits to the Variable Range Hopping (VRH) of Mott type model. Carrier localization length, L, obtained from VRH plots, decreases from 4.6 A for x=0.05 to 3.9 A for the x=0.20 sample. In the metallic region, the n term in the resistivity fits to the Zener-Double exchange polynomial law (ρ=ρ0+ρ2T2+ρnTn) increases from n=5.5 for x=0.05 to n=7.5 for x=0.15. From magnetic susceptiblity measureme...

Improvement in resistive switching of Ba-doped BiFeO3 films

We investigate the resistive switching behavior of Ba-doped BiFeO3 (BBFO) films grown on single crystalline SrTi0.99Nb0.01O3 substrates. Observation of diode like I-V behavior and reduction in VC with Ba-content in BBFO films have been understood in the context of modifications in its energy band diagram. Also, I-V curves exhibit hysteresis which has been explained on the basis of migration and recombination of oxygen vacancies under field conditions. Furthermore, increment in Ba-content improves the retention property and ON/OFF switching ratio in BFO films which makes them suitable for applications in switching devices.

Structural, microstructural, transport, and magnetotransport properties of nanostructured La0.7Sr0.3MnO3 manganites synthesized by coprecipitation

The structural, transport, and magnetotransport properties of single-phase, homogeneous nanostructured La0.7Sr0.3MnO3 (LSMO) manganites synthesized by the coprecipitation route were investigated and the effect of sintering temperature on the microstructure of LSMO compounds was studied. A strong dependence of transport and magnetotransport behavior on the microstructure and nature of grain boundaries has been observed in the single-phase LSMO sintered at various temperatures. High-field magnetoresistance (HFMR) at room temperature is found to increase [13% (LS6) to 25% (LS9)] while low temperature (5 K) magnetoresistance decreases [75% (LS6) to 46% (LS9)] under 9 T field with increase in sintering temperature, which has been attributed to the spin-polarized tunneling and spin-dependent scattering of charge carriers.

Thickness dependent swift heavy ion irradiation effects on electronic transport of (La0.5Pr0.2)Ba0.3MnO3 thin films

Electrical resistivity and magnetoresistance measurements on (La0.5Pr0.2)Ba0.3MnO3 thin films of 50 and 200nm thicknesses, irradiated by 200MeV Ag+15 ions, have been carried out. Before irradiation, all the films exhibit insulator-metal transition at a temperature (Tp) of ∼200K. After irradiation, both resistivity and Tp remain mostly unaffected in 50nm thin film but vary largely in 200nm thin films. This disparity in irradiation effect on these films is explained to arise from the interplay of columnar defect induced (i) enhancement in resistivity with increasing thickness of the film and (ii) local release of strain at the interfaces of low thickness films, which decreases resistivity.

Influence of hole filling by Co and hole doping by Ca on the superconductivity of ErBa2Cu3O7−δ

Abstract The structural and superconducting properties of (Er1−yCay)Ba2 (Cu1−xCox)3Oz samples are investigated using X-ray diffraction, resistivity and oxygen content measurements. The effect of increasing Co concentration in ErBa2(Cu1−xCox)3Oz lowers the carrier concentration and decreases Tc, which is attributed to hole filling by Co. This suppression of Tc has been compensated by appropriate hole doping with Ca, for instance, in the oxide (Er1−yCay)Ba2(Cu0.94Co0.06)3Oz, the Tc increases from 34 K (y = 0.0) to 85 K (y = 0.18, compensated oxide) as the hole filling by Co is completely balanced by hole doping from Ca.

Suppression of superconductivity in the (Er1-x-yPrxCay)Ba2Cu3O7- delta (O<or=(x, y)<or= 0.3) system

Pr- and Ca-substituted (Er1-x-yPrxCay)Ba2Cu3O7- delta superconductors have been prepared under identical conditions and characterized according to resistivity and AC susceptibility measurements. The observed reduction of Tc with x in (Er1-xPrx)Ba2Cu3O6.90 for 0<or=x<or=0.3 can be described by an empirical relation which incorporates the filling (or localization) of mobile holes in the CuO2 planes and magnetic pair breaking by local moments. In a similar way, the observed lowering of Tc with increasing y in (Er1-yCay)Ba2Cu3O7- delta provides convincing evidence that superconducting electron pair breaking and hole doping are responsible for the suppression of superconductivity by Ca.

Size-controlled electrical properties of sol–gel-grown nanostructured Gd0.95Ca0.05MnO3

In this communication, we report the results of the studies on electrical properties of cost-effective modified sol–gel-grown nanostructured Gd0.95Ca0.05MnO3 (GCMO) manganites sintered at different temperatures. Structural investigations, carried out using X-ray diffraction measurements, reveal the single-phasic nature of GCMO samples having orthorhombic unit cell structure. Frequency-dependent variation in AC conductivity (σAC) has been discussed on the basis of correlated barrier hopping (CBH) mechanism for the GCMO samples sintered at lower temperatures. Sintering temperature-induced transition from CBH mechanism to Maxwell–Wagner relaxation processes has been discussed in detail. Size-induced modifications in the impedance response of the samples have been understood, in detail, using size effects and Cole–Cole plots.Graphical Abstract

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 200MeV Ag+15 ions with a maximum ion dose up to 1×1012ions∕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 1×1012ions∕cm2 suppresses resistivity by factors of 3 and 10 at 330K [insulator-metal (I-M) transition] and at 10K, respectively. On the other hand, with increasing ion dose, the magnetoresistance 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.

Role of Calcium in the Evolution of Superconductivity in a (La2−xRx)Ba2(CayCu4+y)Oz (R = Y, Er, Gd) System

It has been reported that, by adding equal amounts of CaO and CuO to non superconducting La3Ba3Cu6Oz (La-336), a series of superconductors with nominal compositions La3CayBa3Cu6+yOz were prepared with maximum Tonc ∼ 80K. Similar studies on addition of CaO and CuO in nonsuperconducting LaBaCu2Oz (La-112) resulted into superconducting LaCaBaCu3Oz (La-1113). To date no attempt has been made to synthesize La2CaBa2Cu5Oz (La-2125) superconducting phase by addition of CaO and CuO to non superconducting La2Ba2Cu4Oz (La-224) system. Also no reports are published to study the effect of replacing larger La3+-ions (1.01Å) by smaller rare earth ions viz Y3+(0.89Å), Er3+(0.91Å), Gd3+(0.91Å) on the structural and superconducting properties of (La2−xRx)Ba2(CayCu4+y)Oz (LRBCaC); 0.0 ≤ x ≤ 0.5; y=2x system. In this paper, we report the method of synthesis, structural and superconducting property characterization using X-ray diffraction, oxygen content measurements using iodometry, resistivity measurements using d.c. four probe technique and a.c. susceptibility measurements in the temperature range RT to 15K. Also a comparative study, on the evolution of superconducting phase with Ca-concentration for different rare earth substitutions for LRBCaC system in the context of hole doping mechanism, is carried out.

Sharp step-like metamagnetic transition in the charge-ordered manganite compound (La0.3Eu0.2)(Ca0.3Sr0.2)MnO3

We have performed transport, magnetization and specific heat measurements on the ABO3-type half-doped (La0.3Eu0.2)(Ca0.3Sr0.2)MnO3 (LECSMO) manganite. At T = 2 K, a sharp step-like metamagnetic transition in the magnetization with a critical field of 3.3 T is observed. The transition is much sharper than that seen at higher temperatures ( K). Such step-like transitions have previously been reported only in Pr-based manganites, but the present data show that the step-like metamagnetism can also be found in other manganite compounds.