The aging of Y1Ba2Cu3O7-δ thin film structures after low energy 30 keV electron irradiation has been investigated. The irradiation was aimed at creating artificial channels with suppressed superconductivity that would enforce the coherent flow of vortices. Through transport measurements, the irradiated regions were found to degrade gradually with the time of aging contrary to non-irradiated parts with good time stability of superconducting properties. Raman spectroscopy and atomic force microscopy investigations have revealed the presence of a relatively thick carbon contamination layer on the top of YBCO films originating from electron irradiation. X-ray photoelectron spectroscopy analysis supported by the evolution of Raman spectra suggests that carbon penetrating YBCO structures may be responsible for chemical interaction with the YBCO species to form C-O bonds, following the time evolution of the Raman spectra.

Transparent conducting Al-doped ZnO films were grown by atomic layer deposition (ALD). Al-doping was introduced by inserting 1 Al2O3 cycle per 28 ZnO cycles. The x-ray photoelectron spectroscopy showed that the density of the Al donors is 2×1021–3×1021 cm−3, while the Hall-effect measurements showed a ten times lower electron density. This low doping efficiency is a well-known inherent problem of the ALD method, and we wanted to explain its origin. We have found that the electron density is reduced by electron traps at the grain surface; however, the effect was too weak to explain the low doping efficiency. Therefore, the mechanism of the Al2O3 doping was analyzed. We have proposed that each Al2O3 molecule ideally provides two single-electron Al donors accompanied by one Zn vacancy, which acts as a two-electron acceptor. This would cause a perfect compensation; however, the compensation is in reality not perfect, which results in weakly efficient doping. Calculations also showed that each Zn vacancy creates a bound pair with an Al donor. To verify our doping model experimentally, it was inserted into the metallic transport theory and compared with the electron transport measurements. A good agreement was found for a broad range of experimental conditions. In the regime of weak localization, the conductivity showed the temperature dependence σ(T)=a+bT3/4, which is a signature of weak localization and electron–electron scattering in a 3D dirty metal.

High resolution X-ray measurements were used to characterize the crystalline structure of La0.67Sr0.33MnO3 (LSMO) thin films grown on La0.26Sr0.76Al0.61Ta0.37O3 (LSAT) substrate under a small compressive strain (-0.2%). The accommodation of lattice mismatch gives rise to a lattice modulation in the structure. A series of linear h scans (rocking curves) across LSMO 004 diffraction for various values of phi angle (rotation of sample around [001] axis) was performed to provide better insight into this structural feature. Despite the cubic structure of the substrate the stress relief mechanism of the LSMO film is considerably anisotropic. Whereas in [010] substrate direction no LSMO lattice modulation was observed, in [100] direction a lattice modulation was developed having no influence on good electrical properties of the prepared LSMO films.

The transition temperature, TC, of two types of optimally doped cuprate high-TC superconductor films, YBa2Cu3O7-δ and La1.85Sr0.15CuO4, is found to increase upon linking Au nanoparticles to their surface via organic molecules. At the same time, and quite surprisingly, the critical current is reduced. We attribute these results to screening of the Coulomb interactions and smearing the pinning potential landscape. The transition temperature was increased also when the Au NPs were not chemically linked to the surface, consistent with the screening scenario. The linking molecules, however, enable selective adsorption of the gold nanoparticles and their separation from the surface, thus eliminating the conventional proximity effect.

The electrical transport effects in interfaces of high TC superconducting and ferromagnetic thin film bilayer structures (YBa2Cu3Ox/La0.67Sr0.33MnO3 junctions with areas of ∼0.2 × 10−4 cm2 and ∼1.21 × 10−4 cm2) were investigated in view of the importance of such structures for oxide electronics and spintronics applications. In some structures the junction resistance Rj, measured by a standard four probe method at T < TC, can be significantly lower (even a few orders) than the real interface resistance Rif because of which a wrong interpretation of the last may occur. We show how to evaluate the right interface resistance and the real Rif was determined from the measurement of RJ for the above two junctions. An unordinary effect - a “change” of the sign of the I-V characteristics in dependence on the current I0 flowing across the bilayer junction was observed in our experiments. We explained the essence of the effect and quantitatively described the effect using a model, proposed in the paper. The conditions for observation of a “negative” value of RJ at T > TC were discussed as well.

The properties of a La0.67Sr0.33MnO3 (LSMO)/YBa2Cu3O7-δ (YBCO) interface in thin film LSMO/YBCO cross-strip type junctions were investigated by means of electrical transport measurements. Resistance vs. temperature and current-voltage dependences, as well as conductance spectra, were used to characterize the electrical parameters of the interface. The results indicated a low resistance (below 10 Ω), while the dielectric properties of the interface pointed to the presence of a 10-nm wide and 40-meV high dielectric potential barrier. The oxygen vacancies in both LSMO and YBCO films at the interface and the charge transfer through the interface were both considered to explain the insulating character of the LSMO/YBCO interface.

We have prepared Nb thin film (thickness 80-100 nm) nanoSQUID with two symmetrically placed nanosized constrictions in superconducting loop. The nanoSQUID was prepared in two steps: at first a microsized SQUID was prepared and in the second step nanosized constrictions of the width of 120 nm in the SQUID loop were created by a focused ion beam technique. We studied the electrical and magnetic properties. From the obtained results, SQUID and constriction dimensions, the spin sensitivity was estimated to be about 50 PB Hz(-1/2). Further improvement of spin sensitivity is possible by lowering the SQUID and constriction dimensions.

The lateral superconductor-ferromagnet-superconductor (SFS) nanojunctions based on high critical temperature superconductor YBa2Cu3O (YBCO) and half-metallic ferromagnet La0.67Sr0.33MnO3 (LSMO) thin films were prepared to investigate a possible presence of long range triplet component (LRTC) of Cooper pairs in the LSMO. We applied Ga3+ focused ion beam patterning to create YBCO/LSMO/YBCO lateral type nanojunctions with LSMO length as small as 40 nm. The resistivity vs. temperature, critical current density vs. temperature and resistance vs. magnetic field dependence were studied to recognize the LRTC of Cooper pairs in the LSMO. A non-monotonic temperature dependence of junction critical current density and a decrease of the SFS nanojunction resistance in increased magnetic field were observed. Only weak manifestations of LRTC and some qualitative agreement with theory were found out in SFS nanojunctions realized from the perovskite materials. The presence of equal-spin triplet component of Cooper pairs in half-metallic LSMO ferromagnet is not such apparent as in SFS junctions prepared from low temperature superconductors NbTiN and half-metallic ferromagnet CrO2. (C) 2016 Elsevier B.V. All rights reserved.

Samples containing the ferromagnetic manganite La0.67Sr0.33MnO3 (LSMO) and high temperature superconducting YBa2Cu3O7 (YBCO) single thin film areas and YBCO LSMO bilayer area were prepared on LaAIO(3) (LAO) substrates and were used for investigation of the electrical properties of the interface. The measurements in the YBCO/LSMO interface demonstrated "negative" values of the resistance. A good interpretation of the obtained results was performed in the framework of a 1D model, which took into account the resistance of the interface R-if and the temperature dependence of the resistance of YBCO and LSMO films. It was shown that the effect of "negative" resistance arises because of the redistribution of the measuring electrical current in the interphase area if the resistance of the interface R-if is small in comparison with the resistances of the neighboring electrodes.

Epitaxial manganite La0.67Sr0.33MnO3 (LSMO) layers, with a thickness of 20-50 nm, are prepared on single crystal (001) SrTiO3 (STO) substrates by pulsed laser deposition technique. Structural characterization (composition analysis, surface morphology), investigated by the Rutherford backscattering spectroscopy and atomic force microscopy, reveals the growth of stoichiometric LSMO films With a smooth surface (root-mean-square value of 0.21-1.6 nm). The prepared LSMO films possess high Curie temperature (approximate to 412 K), low room temperature resistivity (1-2 m Omega cm) and maximum of temperature coefficient of resistivity TCR = 2.7% K-1 at 321 K.

Temperature dependences of the resistivity of manganite La0.7Ca0.3MnO3 (LCMO) films deposited on LaAlO3 and SrTiO3 substrates by RF magnetron sputtering were shown to be successfully simulated in the whole temperature range (covering metal, insulator and metalinsulator transition regions) using a phenomenological phase-coexistence transport model. Quantitative data on the internal parameters of these films were obtained. The possibility was also considered for investigation of individual resistive characteristics and excess conductivity of a high temperature superconducting (HTS) YBa2Cu3O7-x (YBCO) thin film in the vicinity of T-C included into a YBCO/LCMO bilayer structure. It was shown that the considered YBCO film in the temperature range from 85.5 K to 114.9 K behaves as a two-dimensional system with respect to the fluctuations in the superconducting order parameter, while a three-dimensional regime is observed in a narrow range of temperatures at T < 85.5 K. Such behavior was assumed to be partly due to the FM LCMO component of the bilayer, the spin-polarized charge carriers of which enter into the YBCO film and cause a "breaking" of superconducting pairs in the superconducting gap and pseudogap regimes.

We present the preparation of bilayers from high-temperature superconductors (HTS) and half-metallic ferromagnetic (FM) manganite with a colossal magnetoresistance (CMR). We used YBa2Cu3O7-x (YBCO) and Tl2Ba2CaCu2O8 (TBCCO) thin films as a HTS material and La0.67Sr0.33MnO3 (LSMO) film as a CMR material. In the case of YBCO/LSMO, we prepared FM/HTS heterostructure for studying the spin-polarized current injection effect on the electrical properties of the YBCO strip in dc or low-frequency regimes and on the microwave characteristics of the strip. For the first time, we report the preparation of a TBCCO/LSMO bilayer. In some applications, the TBCCO offers better parameters (higher working temperature, lower surface resistance, lower 1/f noise) than YBCO.

A metallic ferromagnet (F) in proximity with a superconductor (S) can transport supercurrent on a long distance through conversion of opposite-spin singlet Cooper pairs (CP) into equal-spin triplet CP (long range triplet component, LRTC), which are not broken by the exchange energy of F. The optimal conditions for the conversion are yet to be clarified; however, it is accepted that the key point to this process include high interface transparency and magnetic inhomogeneity at the SF interface. The aim of our paper is to study SF nanostrips (length of about 1500 nm and width down to 300 nm) and lateral SFS nanojunctions based on high critical temperature YBa2Cu3Ox (YBCO) and half-metallic La0.67Sr0.33MnO3 (LSMO) thin films. We applied a focused Ga+ ion beam (FIB) for patterning the SF nanostrips, as well as lateral SFS nanojunctions, by creating a slot in the nanostrip after removing the YBCO film in the slot along a length of about 200 nm. The temperature dependences of the samples resistance R(T) show critical temperature TCn ≈ 89 K of the SF nanostrips; however, the SFS nanojunctions at T < TCn show a residual resistance R < 100 Ω corresponding to a dirty LSMO (ρ≈ 10 mΩ cm) in the slot. The LRTC was not observed in our lateral SFS nanojunctions until now.

We investigated structural, electrical and magnetic properties of epitaxial La0.67Sr0.33MnO3 (LSMO) thin films (20-100 nm thick) deposited by pulsed laser ablation on different substrates. Single crystalline substrates: (001) SrTiO3, (001) LaAlO3, (001) La0.26Sr0.76Al0.61Ta0.37O3 and (001) MgO were used to vary the substrate-induced epitaxial strain. The LSMO films exhibit very good crystal quality and enhanced temperatures of metal-insulator transition (T-MI) as well as temperature of ferromagnetic ordering (Curie temperature, T-C) up to 451 K with T-MI = T-C coincidence of both temperatures. The enhanced T-C (T-MI) values were analyzed with respect to substrate-induced strain and LSMO film thickness. We ascribe the increased T-C (T-MI) values to decreasing strength of electron-phonon coupling coming from Jahn Teller splitting. The substrate-induced strain in the LSMO films only decreased the T-C (T-MI) values depending on magnitude of biaxial strain. (C) 2016 Elsevier Ltd. All rights reserved.

Effects of low energy 30 keV electron irradiation of superconducting YBa2Cu3O7-delta thin films have been investigated by means of transport and micro-Raman spectroscopy measurements. The critical temperature and the critical current of 200 nm thick films initially increase with increasing fluency of the electron irradiation, reach the maximum at fluency 3 4 x 10(20) electrons/cm(2), and then decrease with further fluency increase. In much thinner films (75 nm), the critical temperature increases while the critical current decreases after low energy electron irradiation with fluencies below 10(20) electrons/cm(2). The Raman investigations suggest that critical temperature increase in irradiated films is due to healing of broken Cu-O chains that results in increased carrier's concentration in superconducting CuO2 planes. Changes in the critical current are controlled by changes in the density of oxygen vacancies acting as effective pinning centers for flux vortices. The effects of low energy electron irradiation of YBCO turned out to result from a subtle balance of many processes involving oxygen removal, both by thermal activation and kick-off processes, and ordering of chains environment by incident electrons. (C) 2016 Elsevier B.V. All rights reserved.

Using dc on-axis magnetron sputtering and pulsed laser deposition, we have grown thin films of La0.67Sr0.33MnO3 (LSMO) on (001) MgO substrates exhibiting a sizeable increase of the metal–insulator transition temperature. In spite of large lattice misfit (8%) between the LSMO film and the substrate structural analyses reveal an epitaxial growth of the films with different crystal structures depending on the used deposition techniques. This work provides structural and electrical characterizations of the LSMO films suitable for further practical applications operating at room temperature.

Thin films of thallium based superconductors were prepared successfully using sputtering target fabricated as a mixture of barium fluoride, calcium fluoride and copper oxide. Such a target is stable, does not degrade and does not involve any special handling (vacuum or argon atmosphere storage). Precursor films sputtered from this target contained less than 5 at.% of fluorine so no fluorine content reduction is needed. Depending on the substrate, film thickness and synthesis conditions, Tl-2212 phase or a mixture of Tl-2212 and Tl-2223 phases was prepared. Although Tl-2212 phase has epitaxial character, Tl-2223 phase, growing on the top of Tl-2212, is only c-axis oriented. The highest values of T-CO were obtained using 300 nm thick precursor films thallinated at 860 degrees C. After the thallination the films contained a mixture of Tl-2212 and Tl-2223 phase with a critical temperature of T-CO = 106 K and a critical current density (at 77 K) up to 6 x 10(4) A/cm(2). Lower T-CO and J(C) values suggest that further optimization of the film synthesis is needed; however, the first results show that the stable sputtering target prepared from fluorides is a good candidate for high quality Tl-based thin film fabrication. (C) 2015 Elsevier Ltd. All rights reserved.

Tl-based cuprate superconducting films were prepared in a two-step process by RF magnetron sputtering of an amorphous precursor and ex situ thallination in open system. The films prepared on LaAlO3 and CeO2 buffered R-plane sapphire substrates consisted from c-axis oriented T1-2212 superconducting phase. The zero resistance critical temperature To exhibited values up to 94K. Subsequently, superconducting structures were prepared from the Tl-based thin films using photolithography process and wet etching. A new etchant based on potassium iodide was used for the Tl-based film patterning. The prepared structures had sharp edges, unchanged phase composition and critical temperature values. Such a way of the Tlbased film patterning is very simple, fast and easy to realize. (C) 2014 Elsevier B.V. All rights reserved.