Nanogranular MgB2 thin films on SiC buffered Si substrates prepared by in-situ method

MgB2 thin films were deposited on SiC buffered Si substrates by sequential electron beam evaporation of B-Mg bilayer followed by in-situ annealing. The application of a SiC buffer layer enables the maximum annealing temperature of 830 C. The Transmission Electron Microscopy analysis confirms the growth of a nanogranular MgB2 film and the presence of a Mg2Si compound at the surface of the film. The 150-200 nm thick films show a maximum zero resistance critical temperature TC0 above 37 K and a critical current density JC ~ 106 A/cm2 at 11K.Comment: 7 pages, 6 figures, submitted to Applied Physics Letter

Electrical and structural properties of MgB2 films prepared by sequential deposition of B and Mg on the NbN buffered Si(100) substrate

We introduce a simple method of an MgB2 film preparation using sequential electron-beam evaporation of B-Mg two-layer (followed by in-situ annealing) on the NbN buffered Si(100) substrate. The Transmission Electron Microscopy analyses confirm a growth of homogeneous nanogranular MgB2 films without the presence of crystalline MgO. A sensitive measurement of temperature dependence of microwave losses shows a presence of intergranular weak links close the superconducting transition only. The MgB2 films obtained, about 200 nm thick, exhibit a maximum zero resistance critical temperature of 36 K and critical current density of 3x10^7 A/cm^2 at 13.2 KComment: 11 pages, 6 figures, submitted to Appl. Phys. Let

Approximation of Electrical and Magneto Transport Properties of LSMO Thin Films

We have used a three term polynomial expression to approximate electrical and magneto transport properties of epitaxial $La_{0.67}Sr_{0.33}MnO_{3}$ (LSMO) thin films in wide temperature range (2-350 K) and in magnetic field up to 9 T. The first term is determined by a low temperature (T<20 K) residual resistivity $ρ_{0}$ and this term is magnetic field independent. The second term describes the electron-electron scattering in LSMO, it shows ~ $T^{2}$ dependence of resistivity up to temperature about 160 K and depends only weakly on magnetic field. The third term, proportional to ~ $T^{4.5}$ dependence, describes a significant increase of resistivity in temperature range 160-350 K and due to its sensitivity to applied magnetic field it is possible to approximate temperature dependence of magnetorestivity below 350 K

LSMO Films with Increased Temperature of MI Transition

Epitaxial $La_{0.67}Sr_{0.33}MnO_{3}$ thin films with a significant increased temperature of metal-insulator transition (~450 K) are prepared on single crystal MgO (001) substrates using different deposition techniques - a dc magnetron sputtering or a pulsed laser deposition. The crystalline perfection of the films is characterized by X-ray diffraction technique (rocking curve measurements and reciprocal space maps). As a consequence of different methods of the film preparation we show various types of the LSMO crystal structure. Our results indicate that all the LSMO layers grown on the MgO substrate with a lattice misfit of about 8% are relaxed

DC nanoSQUID from Nb thin films

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 μ_{B} Hz^{-1/2}. Further improvement of spin sensitivity is possible by lowering the SQUID and constriction dimensions

LSMO/YBCO heterostructures and investigation of "negative" resistance effect in the interface

Samples containing the ferromagnetic manganite La_{0.67}Sr_{0.33}MnO₃ (LSMO) and high temperature superconducting YBa₂Cu₃O₇ (YBCO) single thin film areas and YBCO/LSMO bilayer area were prepared on LaAlO₃ (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

Characterization of epitaxial LSMO films grown on STO substrates

Epitaxial manganite La_{0.67}Sr_{0.33}MnO₃ (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 ( ≈ 412 K), low room temperature resistivity (1-2 mΩ cm) and maximum of temperature coefficient of resistivity TCR = 2.7% K¯¹ at 321 K