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We report a systematic study about the thickness and microstructure influence on the mechanical properties of nanocrystalline Cu thin films grown by DC sputtering. Mechanical properties were determined by using atomic force microscopy-assisted nanoindentation. Results showed a clear decrease of the elastic modulus and indentation hardness as the film thickness and grain size increase. Annealing time as well as the temperature seem to affect the mechanical behavior of the films by inducing microstructural changes, producing comparable changes to those produced by size effects (film thickness). Results suggest that both effects are important to explain the mechanical behavior of polycrystalline thin films. This work helps understanding what physical mechanisms play a fundamental role on the mechanical behavior of thin films.

A systematic finite element analysis (FEA) of conical indentation in different isotropic elastic-plastic bulk solids was realized. In particular, the relation between the indentation Hardness (H)-to-Reduced Elastic Modulus (Er) ratio and the Elastic (Ue)-to-Total (Ut) strain energy ratio was studied. Results showed a linear dependency between both ratios as predicted by analytical studies, being the proportionality constant mainly dependent on cone semi-angle(𝜃) and material Poisson´s ratio (𝑣). A well-agreement with experimental data reported in the literature was observed for a wide variety of materials. By a simple analysis of the Oliver & Pharr method and our results, we proposed two analytical equations to calculate the H and E parameters overcoming the indenter contact area (AC) dependence in indentation data analysis. AC independent analytical procedures can become interesting to simplify the data analysis and overcome considerable uncertainties due to possible pile-up effects associated to different plastic deformation phenomena.

We study the electrical transport of vertically-stacked Josephson tunnel junctions using GdBa$_2$Cu$_3$O$_{7-d}$ electrodes and a BaTiO$_3$ barrier with thicknesses between 1 nm and 3 nm. The junctions with an area of 20 mm x 20 mm were fabricated combining optical lithography and ion etching using GdBa$_2$Cu$_3$O$_{7-d}$ (16 nm) / BaTiO$_3$ (1 - 3 nm) / GdBa$_2$Cu$_3$O$_{7-d}$ (16 nm) trilayers growth by sputtering on (100) SrTiO$_3$. Current-voltage measurements at low temperatures show a Josephson coupling for junctions with BaTiO$_3$ barriers of 1 nm and 2 nm. Reducing the barrier thickness bellow a critical thickness seems to suppress the ferroelectric nature of the BaTiO$_3$. The Josephson coupling temperature is strongly reduced for increasing barrier thicknesses, which may be related to the suppression of the superconducting critical temperature in the bottom GdBa$_2$Cu$_3$O$_{7-d}$ due to stress. The Josephson energies at 12 K are of $\approx$ 1.5 mV and $\approx$ 7.5 mV for BaTiO$_3$ barriers of 1 nm and 2 nm. Fraunhofer patterns are consistent with fluctuations in the critical current due to structural inhomogeneities in the barriers. Our results are promising for the development of Josephson junctions using high-T$_c$ electrodes with energy gaps much higher than those usually present in conventional low-temperature superconductors.

We study the thickness influence on the martensitic transformation in Cu-Al-Ni thin films grown by sputtering on Si (001). Thin films with thicknesses between 0.1 μm and 2.25 μm were grown at 563 K. The analysis of the microstructure reveals a columnar growth with preferred orientation Cu-Al-Ni L21 (001)[100] //Si (001)[100]. The martensitic transformation is strongly suppressed for films thinner than 1.3μm, which can be related with an interfacial layer imposing restitutive forces. This is evidenced in the extended transformation / retransformation ranges and in the absence of hysteresis for 0.15 μm thick films

We study the mechanical properties of Cu thin films on Si (100) by performing nano-indentation using an atomic force microscopy. Cu films with thickness of 0.3 µm, 1 µm and 2 µm were analyzed. Area profile studies let us understand the critical influence of the indenter geometry uncertainty on the estimation of the mechanical properties. This seems to be very important when studying thin films because penetrations depths are very small and close to the indenter apex which could have geometrical discontinuities. We found that the hardness of the samples and Young modulus decreases as the film thickness increases. The origin of this behavior could be ascribed to a substrate-film mechanical coupling or a microstructural effect.

A systematic finite element analysis (FEA) of conical indentation in different isotropic elastic-plastic bulk solids was realized. In particular, the relation between the indentation Hardness (H)-to-Reduced Elastic Modulus (Er) ratio and the Elastic (Ue)-to-Total (Ut) strain energy ratio was studied. Results showed a linear dependency between both ratios as predicted by analytical studies, being the proportionality constant mainly dependent on cone semi-angle (θ) and material Poisson´s ratio (ν). A well-agreement with experimental data reported in the literature was observed for a wide variety of materials. By a simple analysis of the Oliver & Pharr method and our results, we proposed two analytical equations to calculate the H and Er parameters overcoming the indenter contact area (AC) dependence in indentation data analysis. AC-independent analytical procedures can become interesting to simplify the data analysis and overcome considerable uncertainties due to possible pile-up effects associated with different plastic deformation phenomena.

La0·8Ba0·2MnO3, Ba0·25Sr0·75TiO3 and BaTiO3 superlattices were grown to study the influence of structural disorder on the physical properties of multiferroic multilayers. Controlling the lattice mismatch of the superlattices allowed growing structures with different growth mechanisms. The manganite layers in the samples were used as “sensor layers”, that respond to the structural changes in the superlattices, induced by changing the thickness and nature of the ferroelectric layers. Stress has a weak influence on the magnetic properties of these systems. Transport properties are characterized by a high temperature thermally activated regime and a low temperature variable hopping one. The strain and structural disorder in the samples increases the localization energy of the current carriers for both regimes. Important interface effects can be achieved controlling the strain and disorder in the interfaces, allowing tuning the metal-insulator transition temperature. These results help to further understand the role of interface effects in the development of manganite based ferromagnetic/ferroelectric multilayered systems.

Cu thin films are nowadays attractive components for emergent MEMS based technologies because their high electrical conductivity ( σ ) and good mechanical properties. In general, σ is negatively affected when the film thickness ( t ) decreases close to the electron mean free path ( l e ) scale and the mechanical resistance is favored. So, we propose a study of the Cu thin films optimum size conditions to achieve a well-compromise between the mechanical and electrical performance. Films mechanical behavior was studied by Atomic Force Microscopy (AFM) assisted nanoindentation. Results showed considerable increments of the elastic ( U e )-to-total ( U t ) strain energy ratios ( U e / U t ) from 0.27 ± 0.02 up to 0.54 ± 0.04 as t was decreased from 2 [µm] to 100 [nm], evidencing a clear films mechanical resistance improvement by reducing t . Our analysis showed that the improvement of the films mechanical resistance easily compensates the negative impact on the electrical conductivity, especially for t > l e .

Oxygen vacancies in oxides nanostructures are the origin of many intriguing phenomena. We have studied the influence of the oxygen pressure in the tunneling properties of a ferroelectric barrier, Ba0.25Sr0.75TiO3 (BSTO), grown over a ferromagnetic electrode. A phenomenological model description was used to obtain critical information about the structure and electrical properties of ultra-thin BSTO layers using conductive atomic force microscopy. The BSTO layers present good insulation properties. Reducing the oxygen content increases the conductivity of the samples. The tunneling of the current carriers is probably the main conduction mechanism for samples with higher barrier thicknesses. Fil: Gonzalez Sutter, Jesus Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Neñer, Lucas. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Navarro, H.. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Leyva, G.. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina Fil: Fusil, S.. Centre National de la Recherche Scientifique; Francia Fil: Bouzehouane, K.. Centre National de la Recherche Scientifique; Francia Fil: Haberkorn, Nestor Fabian. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Sirena, Martin. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina

We report the electrical transport in vertical Josephson tunnel junctions (area 400 $\mu m$$^2$) using GdBa$_2$Cu$_3$O$_7$$_{-\delta}$ electrodes and SrTiO$_3$ as an insulating barrier (with thicknesses between 1 nm and 4 nm). The results show Josephson coupling for junctions with SrTiO$_3$ barriers of 1 nm and 2 nm. The latter displays a Josephson of 8.9 mV at 12 K. This value is larger than the usually observed in planar arrays of junctions. Our results are promising for the development of superconducting electronic devices in the terahertz regime., Comment: 15 pages, 4 figures

The martensitic transformation of polycrystalline thin films based on shape memory alloys is usually affected by the average grain size and by the thickness. We have carried out a study of the temperature driven martensitic transformation in micrometric grain size Cu-Al-Ni films with 18R structure. Thin films with a thickness of 6 μm were grown by sputtering on highly oriented pyrolytic graphite HOPG (0001) substrate at 873 K. After that, the samples were peeled-off from the substrate and annealed at 1123 K for 30 min. The observed microstructure shows an average grain size of 3.7 (± 0.2) μm. The martensitic start temperature (M s) for different films ranges from 170 K to 370 K due to small changes in the chemical concentration. The influence of surface oxides and changes in the atomic order produced by post-quench aging treatments is analyzed. The results show that while surface passivation has a weak influence, changes in the atomic order increase M s without impacting significantly on the hysteresis. Comparison with previous results of nanometric and micrometric grain size samples reveals that the barriers for the transformation are mainly given by plastic deformation at grain boundaries. Fil: Morán, Mauricio Javier. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Condo, Adriana Maria. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Bengió, Silvina. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Soldera, Flavio Andres. Universitat Saarland; Alemania Fil: Sirena, Martin. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Haberkorn, Nestor Fabian. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina

We report the precise control of tunneling magnetoresistance (TMR) in devices of self-assembled core/shell Fe$_3$O$_4$/Co$_{1-x}$Zn$_x$Fe$_2$O$_4$ nanoparticles ($0\leq x\leq 1$). Adjusting the magnetic anisotropy through the content of Co$^{2+}$ in the shell, provides an accurate tool to control the switching field between the bistable states of the TMR. In this way, different combinations of soft/hard and hard/soft core/shell configurations can be envisaged for optimizing devices with the required magnetotransport response., Comment: 25 pages, 7 figures

We report on the influence of the disorder and stoichiometry in the resulting superconducting critical temperature of γ-Mo2N thin films. Initially, three films (with Tc values of 7.6 K, 6.8 K and 6 K) were grown at room temperature by reactive sputtering, on Si (1 0 0) using different N2/(Ar+N2) mixtures. The influence of the thermal annealing up to 973 K and irradiation damage produced by 1 MeV Zr+(fluence up 2 × 1014 cm−2) is analyzed. The Tc of pristine films remains unchanged for increasing irradiation doses up 2 × 1014 cm−2. The Tc for annealed films decreases close to the value expected for bulk samples (≈5 K) for increasing the annealing temperature. Successive irradiations of the annealed films tend to increase their Tc up to its initial values (before annealing). The results indicate that the Tc in nanometric grain size γ-Mo2N thin films is affected by both nitrogen stoichiometry and disorder at the atomic scale. Fil: Haberkorn, Nestor Fabian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Bengió, Silvina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Suarez, Sergio Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina Fil: Pérez, Pablo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energí­a Atómica. Gerencia del Area Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Balseiro). División Colisiones Atómicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Hofer, Juan Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina Fil: Sirena, Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina

We studied the elastic properties of free-standing multilayered systems using finite element analysis with a rigid spherical indenter. To model and simulate the elastic response of these systems a 2-dimensional axisymmetric solid model was used. In particular, multilayered systems with a total thickness of 10 [μm] and composed by a periodic bilayer array were studied. The bilayers thickness in each multilayered system, as well as the isotropic elastic constants (Young´s modulus and Poisson´s ratio) of each thin film, were fixed to be constant in all the cases. The influence on the mechanical properties of different relative thickness ratios (from 0.11 up to 9) between the two films in the bilayer was carefully studied. Our results indicated that changes in the relative thickness ratios can produce considerable changes in the elastic mechanical response of the multilayered systems, observing important variations up to 19% (for displacements lower than 10% of the first film thickness) on the magnitude of the effective Young´s modulus. The interplay between the structural properties of the layers gives place to the nonlinear behavior of the Young modulus as a function of the volume fraction of the different layers. Due to the non-homogenous nature of the system, a strong dependence of the sample Young´s modulus with respect to the indentation depth was observed. This work contributes to qualitatively understand the impact of different characteristics of multilayered systems, such as the elastic properties and the proportion of the composing materials, on its elastic behavior.

Lead selenide (PbSe) thin films deposited by aqueous-based chemical methods have recently reached considerable importance for the production of different low cost and good quality optoelectronic devices. Applications in infrared devices as well as in low cost photovoltaic technologies as efficient absorbent layers have been extensively studied. In this work, the synthesis of homogeneous, polycrystalline, low-roughness, electrically conductive and narrow band gap PbSe thin films by using Chemical Bath Deposition (CBD) on glass substrates is reported. The effects of using different NaOH concentrations on the films physical and chemical properties were studied. Structural analysis realized by X-Ray Diffraction (XRD) technique showed the polycrystalline nature of the films, particularly observing a preferred texture. Atomic Force Microscopy (AFM) studies revealed a compact and homogeneous growth of the thin films. A well-defined microstructure and low roughness (varying between 5 and 35 [nm]) were generally observed. Scanning Electron Microscopy (SEM) imaging studies showed the good growth quality of the thin films, observing well-defined film-to-substrate interfaces. Film thickness values between 138 ± 9 and 277 ± 20 [nm] were estimated. Chemical composition analysis realized by Energy Dispersive X-Ray Spectroscopy (EDS) exposed the non-stoichiometric nature of the PbSe films. An atomic concentration predominance of Se with respect to Pb in all samples was observed, suggesting a possible p-type conductivity. Infrared spectrophotometry measurements indicated energy band gaps in the Mid-Infrared Range (MIR), estimating values from 0.326 up to 0.393 [eV]. The thin films generally presented high electrical conductivities with respect to the typical ranges for semiconductors, estimating values in the order of 101 [(Ω·cm)−1]. Results show that the low cost and simple synthesis CBD based procedures can be used to produce high structural and morphological quality PbSe thin films with attractive optoelectronic properties (narrow band gap and electrically conductive) for the potential development of devices in infrared detection industry.

Artificially engineered superlattices were designed and fabricated to induce different growth mechanisms and structural characteristics. DC sputtering was used to grow ferromagnetic (La0.8Ba0.2MnO3)/ferroelectric (Ba0.25Sr0.75TiO3 or BaTiO3) superlattices. We systematically modified the thickness of the ferromagnetic layer to analyze dimensional and structural disorder effects on the superlattices with different structural characteristics. The crystalline structure was characterized by X-ray diffraction and transmission electron microscopy. The magnetic and electronic properties were investigated by SQUID magnetometry and resistance measurements. The results show that both strain and structural disorder can significantly affect the physical properties of the systems. Ba0.25Sr0.75TiO3 based superlattices with a low thickness of the ferromagnetic layers (4 nm) present compressive strain that decreases the ferromagnetic transition temperature from 250 K corresponding to the unstressed samples to 230 K. In these samples, the localization energy of the charge carrier through the electron-phonon interaction decreases at low temperatures (∼100 meV). Ba0.25Sr0.75TiO3 based superlattices with thicknesses of the ferromagnetic layers higher than 12 nm present tensile strain that reduces the charge carrier localization energy at low temperatures (∼1 meV), increasing the ferromagnetic transition temperature (Tc∼265 K). Structural defects in BaTiO3 based superlattices have a stronger influence on the magnetic properties than on the transport properties. Nevertheless, disorder blocks the ferromagnetic transition for highly disordered samples (thickness of the ferromagnetic layer

In order to use the shape memory alloy Cu-Al-Ni in micro-actuators, freestanding thin films with martensitic transformation are required. Here we show that freestanding Cu-Al-Ni thin films with L21 structure, martensitic transformation and shape memory effect can be obtained using iron as a sacrificial layer. The Cu-Al-Ni films with best performance are obtained at deposition temperatures between 533 K and 563 K. The Fe layer can afterwards be removed selectively by electrochemical etching. Fil: Morán, Mauricio Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Condo, Adriana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Soldera, Flavio. Universitat Saarland; Alemania Fil: Sirena, Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Haberkorn, Nestor Fabian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina

Molybdenum oxynitride (MoNxOy) thin films were grown by reactive sputtering on Si (100) substrates at room temperature. The partial pressure of Ar was fixed at 90%, and the remaining 10% was adjusted with mixtures N2:O2 (varying from pure N2 to pure O2). The electrical properties of the films depend on the chemical composition. Thin films grown using mixtures up to 2% O2 have γ-Mo2N phase and display superconductivity. The superconducting critical temperature Tc reduces from ∼6.8 K to below 3.0 K as the oxygen increases. On the other hand, the films are mostly amorphous for gas mixtures above 2% O2. The electrical conductivity shows a semiconductor-like behavior well described by variable-range hopping conduction. The analysis of the optical properties reveals that the samples do not have a defined semiconductor bandgap, indicating that the high structural disorder produces electron excitation for a wide range of energies.

We report on the synthesis and characterization of nanocrystalline delta-MoN by crystallization of amorphous thin films grown on (100) Si by reactive sputtering at room temperature. Films with chemical composition MoN were grown using a deposition pressure of 5mTorr with a reactive mixture of Ar/(Ar+N2)=0.5. The as-grown films display mostly amorphous structure. Nanocrystalline delta-MoN phase is obtained after annealing at temperatures above 600 {\deg}C. The superconducting critical temperature Tc depends on film thickness. Thick films (170 nm) annealed at 700 {\deg}C for 30 min display a Tc = 11.2 K (close to the one reported for bulk specimens: 13 K), which is gradually suppressed to 7.2 K for 40 nm thick delta-MoN films. Our results provide a simple method to synthesize superconducting nitride thin films on silicon wafers with Tc above the ones observed for conventional superconductors such as Nb., Comment: 16 pages, 7 figues

Magnetic shape memory nanostructures have a great potential in the field of the nanoactuators. The relationship between dimensionality, microstructure and magnetism characterizes the materials performance. Here, we study the martensitic transformation in supported and free-standing epitaxial Ni47Mn24Ga29 films grown by sputtering on (0 0 1) MgO using a stoichiometric Ni2MnGa target. The films have a Curie temperature of ~390 K and a martensitic transition temperature of ~120 K. Similar transition temperatures have been observed in films with thicknesses of 1, 3 and 4 μm. Thicker films (with longer deposition time) present a wider martensitic transformation range that can be associated with small gradients in their chemical concentration due to the high vapour pressure of Mn and Ga. The magnetic anisotropy of the films shows a strong change below the martensitic transformation temperature. No features associated with variant reorientation induced by magnetic field have been observed. Annealed films in the ...

This paper provides a systematic analysis of the morphology and the superconducting critical temperature obtained in very thin GdBa 2 Cu 3 O 7 − δ films grown on (0 0 1) SrTiO 3 substrates by DC sputtering. We find that the use of a very thin SrTiO 3 buffer layer (≈2 nm) modify the nucleation of GdBa 2 Cu 3 O 7 − δ on the surface of the substrate reducing the formation of 3 dimensional clusters. Our results demonstrate that 16 nm thick GdBa 2 Cu 3 O 7 − δ films with an average root-mean-square (RMS) smaller than 1 nm and large surface areas (up 10 μm 2 ) free of 3 dimensional topological defects can be obtained. In films thinner than 24 nm the onset (zero resistance) of superconducting transition of the films is reduced, being close to liquid nitrogen. This fact can be associated with stress reducing the orthorhombicity and slightly drop in oxygen stoichiometry.

We study the crystalline structure and superconducting properties of γ-Mo2N thin films grown by reactive DC sputtering on AlN buffered Si (001) substrates. The films were grown at room temperature. The microstructure of the films, which was studied by X-ray diffraction and transmission electron microscopy, shows a single-phase with nanometric grains textured along the (200) direction. The films exhibit highly uniform thickness in areas larger than 20 × 20 μm2. The superconducting critical temperature Tc is suppressed from 6.6 K to ≈ 3.0 K when the thickness decreases from 40 nm to 5 nm. The residual-resistivity ratio is slightly smaller than 1 for all the films, which indicates very short electronic mean free path. The films are in the superconducting dirty limit with upper critical field Hc2 (0) ≈ 12 T for films with thickness of 40 nm, and 9 T for films with thickness of 10 nm. In addition, from the critical current densities Jc in the vortex-free state, we estimate a penetration depth λ(0) ≈ (800 ± 50) nm and a thermodynamic critical field Hc (0) = (500 ± 80 Oe). Fil: Haberkorn, Nestor Fabian. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Bengió, Silvina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Troiani, Horacio Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Suarez, Sergio Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Pérez, Pablo Daniel. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Granell, Pablo Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Industrial; Argentina Fil: Golmar, Federico. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Industrial; Argentina Fil: Sirena, Martin. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Guimpel, Julio Juan. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

We report on the superconducting properties of molybdenum nitride thin films grown by reactive DC sputtering at room temperature with a N2:Ar mixture. Thin films grown using 5 % N2 concentration display Tc = 8 K, which is gradually reduced and abruptly disappears for 40 % N2 concentration. This suppression can be associated with changes in the nitrogen stoichiometry from Mo2N to MoN. Our results provide an effective and simple path to prepare Mo2Nx thin films with tunable Tc, which is relevant for the investigation of the fundamental properties and for technological applications., 7 pages, 3 figures, 1 table, short communication

Here, we report the synthesis of single crystalline β phase Cu–Zn nanowires (diameter around 150 nm and typical length up to 10 μm) by combining electrodeposition and annealing. The obtained nanowires present temperature driven martensitic transformation similar to that found in bulk samples from B2 to 9R structure. A weak influence of the dimensionality on the martensitic transformation is observed in these nanowires. The possibility to obtain bundles of single crystalline nanowires with tunable martensitic transformation temperature and hysteresis similar to that found in bulk, seems to be a fundamental approach to the development of smart nanosystems based on shape memory alloys.

Cd1-xZnxS thin films have been studied extensively as window layers for solar cell applications. However, a mismatch between the Cd1-xZnxS and copper-indium-gallium-selenide absorber layers increases with Zn film concentration, which reduces the device eficiency. In this work, Cd1-xZnxS thin films with low Zn concentrations were analyzed. The effect of the addition of different molar Zn concentrations to the reaction mixture on the growth mechanism of Cd1-xZnxS thin films and the influence of these mechanisms on structural, optical and morphological properties of the films has been studied. Cd1-xZnxS thin films were synthesized by chemical bath deposition using an ammonia-free alkaline solution. Microstructural analysis by X-ray diffraction showed that all deposited films grew with hexagonal structure and crystallite sizes decreased as the Zn concentration in the film increased. Optical measurements indicated a high optical transmission between 75% and 90% for wavelengths above the absorption edge. Band gap value increased from 2.48 eV to 2.62 eV, and the refractive index values for Cd1-xZnxS thin films decreased as the Zn increased. These changes in films and properties are related to a modification in growth mechanism of the Cd1-xZnxS thin films, with the influence of Zn(OH)2 formation being more important as Zn in solution increases., SCOPUS: ar.j, info:eu-repo/semantics/published

The micromagnetic domain structure of MnAs films gave place to an intense research activity in the last few years due to its potential application in magneto-electronic devices such as domain-wall track memories and logic circuits. These applications require a full knowledge of miniaturization effects on the magnetic properties of the material. In this work, X-ray photoemission electron microscopy has been used for imaging magnetic domains in lithographically fabricated MnAs ribbons, addressing the dependence of the domain configuration on film thickness and ribbon width. Our experiments show a transition from head-on to regular stripe domains below a critical width/thickness ratio wc ≈ 6. Micromagnetic simulations suggest that this transition is correlated to the magnetic structure of the surface plane. Depending on the ribbon width and thickness, the magnetic configuration is shown to evolve from flux-closure domain structure to a state of almost homogeneous magnetization, observed for narrower ribbons. The evolution of the domain structure, magnetic fraction, and magnetization with temperature has been studied across the ferromagnetic/paramagnetic transition. Our experiments show that the magnetic configuration in ribbons exhibits higher stability to temperature variations than in as-cast films. Fil: Steren, Laura Beatriz. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Tortarolo, Marina del Carmen. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Fernandez Baldis, Federico Jose. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Sirena, Martin. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Sacchi, M.. Universite de Paris Vi. Institut des Nanosciences de Paris; Francia Fil: Etgens, V. H.. Federation Lavoisier Franklin; Francia Fil: Eddrief, M.. Universite de Paris Vi. Institut des Nanosciences de Paris; Francia Fil: Santos, B.. Elettra-Sincrotrone Trieste; Italia Fil: Mentes, T. O.. Elettra-Sincrotrone Trieste; Italia Fil: Locatelli, A.. Elettra-Sincrotrone Trieste; Italia

We report on the interlayer exchange coupling across insulating barriers observed on Ni80Fe20/Ba0.05Sr0.95TiO3/La0.66Sr0.33MnO3 (Py/BST0.05/LSMO) trilayers. The coupling mechanism has been analyzed in terms of the barrier thickness, samples' substrate, and temperature. We examined the effect of MgO (MGO) and SrTiO3 (STO) (001) single-crystalline substrates on the magnetic coupling and also on the magnetic anisotropies of the samples in order to get a deeper understanding of the magnetism of the structures. We measured a weak coupling mediated by spin-dependent tunneling phenomena whose sign and strength depend on barrier thickness and substrate. An antiferromagnetic (AF) exchange prevails for most of the samples and smoothly increases with the barrier thicknesses as a consequence of the screening effects of the BST0.05. The coupling monotonically increases with temperature in all the samples and this behavior is attributed to thermally assisted mechanisms. The magnetic anisotropy of both magnetic components has a cubic symmetry that in the case of permalloy is added to a small uniaxial component. Fil: Carreira, Santiago José. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Aviles Felix, Luis Steven. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Sirena, Martin. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Alejandro, Gabriela. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Steren, Laura Beatriz. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

We report the influence of the microstructure on the martensitic transformation in polycrystalline Cu-Zn-Al thin films with 18R structure. The films are grown in two steps. First, Cu-Al thin films are obtained by DC sputtering. Second, the Zn is introduced in the Cu-Al thin films by the annealing them together with a bulk Cu-Zn-Al reference. The crystalline structure of the films was analyzed by X-ray diffraction and transmission electron microscopy. The martensitic transformation temperature was measured by electrical transport using conventional four probe geometry. It was observed that temperatures above 973 K are necessary for zincification of the samples to occur. The resulting martensitic transformation and its hysteresis (barrier for the transformation) depend on the grain size, topology and films thickness. Fil: Domenichini, Pablo Exequiel. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Condo, Adriana Maria. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Soldera, F.. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Sirena, Martin. Universitat Saarland; Alemania. Universitat Saarland; Alemania Fil: Haberkorn, Nestor Fabian. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina

We have studied the fabrication of atomic force microscope (AFM) based nanotemplates using electrically controlled indentation (ECI) and a composite barrier (photoresist/alumina) that is resistant to the lithography process and presents good mechanical properties for indentation. The indentation process is affected by several factors such as the indentation speed, the trigger voltage and the barrier type. We have used the nanotemplate technique to fabricate small gold–gold nanocontacts (1–10 nm). In this limit, the size of the contacts that is obtained through the indentation process seems to be stochastic. However, low dimension, clean metallic contacts were achieved with high temporal stability and compatible with low temperature measurements. The fabricated nanotemplates are versatile and can be used in a wide range of applications, from nanojunctions to connecting a single nano-object. Small area metallic contacts can be used to study spin injection or ballistic transport.

The optimization of the superconducting properties in a bottom electrode and the quality of an insulator barrier are the first steps in the development of superconductor/insulator/superconductor tunnel junctions. Here, we study the quality of a BaTiO3 tunnel barrier deposited on a 16γnm thick GdBa2Cu3O7-δ thin film by using conductive atomic force microscopy. We find that the tunnel current is systematically reduced (for equal applied voltage) by increasing the BaTiO3 barrier thickness between 1.6 and 4γnm. The BaTiO3 layers present an energy barrier of 1.2γeV and an attenuation length of 0.35-0.5γnm (depending on the applied voltage). The GdBa2Cu3O7-δ electrode is totally covered by a BaTiO3 thickness above 3γnm. The presence of ferroelectricity was verified by piezoresponse force microscopy for a 4γnm thick BaTiO3 top layer. The superconducting transition temperature of the bilayers is systematically suppressed by increasing the BaTiO3 thickness. This fact can be associated with stress at the interface and a reduction of the orthorhombicity of the GdBa2Cu3O7-δ. The reduction in the orthorhombicity is expected by considering the interface mismatch and it can also be affected by reduced oxygen stoichiometry (poor oxygen diffusion across the BaTiO3 barrier). Fil: Navarro Fernández, Henry Luciano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Yang, Ilkyu. Pohang University of Science and Technology; Corea del Sur Fil: Sirena, Martin. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Kim, Jeehoon. Pohang University of Science and Technology; Corea del Sur. Institute for Basic Science; Corea del Sur Fil: Haberkorn, Nestor Fabian. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina

MnAs thin films present a phase coexistence of regularly arranged ferromagnetic (alfa) and paramagnetic (beta) stripes below the Curie temperature when grown onto GaAs(100) substrates. In this letter, we report the observation of a magneto-structural phase transition induced by magnetic field on MnAs nanoribbons below the Curie temperature. A transformation of high-resistance paramagnetic regions into low-resistance ferromagnetic ones is observed above temperature-dependentcritical magnetic fields. The phenomenon is hysteretic, highly anisotropic, and size dependent and could be the origin of the high magneto-resistance effect observed at temperatures close to room temperature in these systems. Fil: Fernandez Baldis, Federico Jose. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Fundación José A. Balseiro; Argentina Fil: Sirena, Martin. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Fundación José A. Balseiro; Argentina Fil: Steren, Laura Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentina Fil: Etgens, V.H.. Universite de Paris Vi. Institut des Nanosciences de Paris; Francia Fil: Eddrief, M.. Universite de Paris Vi. Institut des Nanosciences de Paris; Francia Fil: Ulysse, C.. Centre National de la Recherche Scientifique; Francia Fil: Faini, G.. Centre National de la Recherche Scientifique; Francia

We have studied the interlayer coupling and the magnetoresistant effect of La0.55Sr0.45MnO3/ La0.67Ca0.33MnO3 structures. Magnetization loops, measured in La0.55Sr0.45MnO3/La0.67Ca0.33MnO3/La0.55Sr0.45MnO3 trilayers, indicate that there is a ferromagnetic coupling of the La0.55Sr0.45MnO3 layers across the La0.67Ca0.33MnO3 spacer up to room temperature, even above the Curie temperature of the La0.67Ca0.33MnO3 layers. However, magnetization versus temperature curves present signatures of the magnetic ordering of both compounds. No extrinsic magnetoresistance associated with the multilayered structure was observed in the whole temperature range due to the presence of the interlayer ferromagnetic coupling.

We report the electrical transport properties of conducting/insulator/conducting heterostructures by studying current-voltage IV curves at room temperature. The measurements were obtained on tunnel junctions with different areas (900, 400 and 100 μm2) using a conducting atomic force microscope. Trilayers with GdBa2Cu3O7 (GBCO) as the bottom electrode, SrTiO3 or BaTiO3 (thicknesses between 1.6 and 4 nm) as the insulator barrier, and GBCO or Nb as the top electrode were grown by DC sputtering on (100) SrTiO3 substrates For SrTiO3 and BaTiO3 barriers, asymmetric IV curves at positive and negative polarization can be obtained using electrodes with different work function. In addition, hysteretic IV curves are obtained for BaTiO3 barriers, which can be ascribed to a combined effect of the FE reversal switching polarization and an oxygen vacancy migration. For GBCO/BaTiO3/GBCO heterostructures, the IV curves correspond to that expected for asymmetric interfaces, which indicates that the disorder affects differently the properties at the bottom and top interfaces. Our results show the role of the interface disorder on the electrical transport of conducting/insulator/conduction heterostructures, which is relevant for different applications, going from resistive switching memories (at room temperature) to Josephson junctions (at low temperatures). Fil: Navarro Fernández, Henry Luciano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Sirena, Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Gonzalez Sutter, Jesus Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Troiani, Horacio Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: del Corro, Pablo Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Granell, Pablo Nicolás. Instituto Nacional de Tecnología Industrial; Argentina Fil: Golmar, Federico. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Haberkorn, Nestor Fabian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina

We report on an experimental and theoretical study of the high-frequency mixing properties of ion-irradiated YBa2Cu3O7 Josephson junctions embedded in THz antennas. We investigated the influence of the local oscillator power and frequency on the device performances. The experimental data are compared with theoretical predictions of the general three-port model for mixers in which the junction is described by the resistively shunted junction model. A good agreement is obtained for the conversion efficiency in different frequency ranges, spanning above and below the characteristic frequencies fc of the junctions. © 2014 AIP Publishing LLC. Fil: Malnou, M.. Laboratoire de Physique et d’Etude des Materiaux; Francia Fil: Feuillet-Palma, C.. Laboratoire de Physique et d’Etude des Materiaux; Francia Fil: Ulysse, C.. Laboratoire de Photonique et de Nanostructures LPN-CNRS; Francia Fil: Faini, G.. Laboratoire de Photonique et de Nanostructures LPN-CNRS; Francia Fil: Febvre, P.. Universite de Savoie; Francia Fil: Sirena, Martin. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Resonancias Magnéticas; Argentina Fil: Olanier, L.. Laboratoire de Physique et d’Etude des Materiaux; Francia Fil: Lesueur, J.. Laboratoire de Physique et d’Etude des Materiaux; Francia Fil: Bergeal, N.. Laboratoire de Physique et d’Etude des Materiaux; Francia

We have studied the thickness dependence of the transport and magnetic properties of strongly textured La0.6Sr0.4MnO3 thin films grown on MgO and SrTiO3, for thickness between 5 and 500 nm. While the resistivity and the magnetoresistance are strongly affected, the magnetization is only moderately changed. The effect on the metal-insulator transition, the low field magnetoresistance and carrier localization is dependent on the substrate, evidencing the effect of the induced defects and strains.

We report structural, magnetic and transport measurements on La0.6Sr0.4MnO3 thin films grown on MgO and TiSrO3 substrates with thickness varying from 5 to 500 nm. We find that the lattice mismatch between substrates and films affects the morphology and induced-strains of the films. We show that these two different effects strongly influence the ferromagnetic order, the metal-insulator transition, the localization of the current carriers and the magnetoresistance of these materials. Fil: Steren, Laura Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Sirena, Martin. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Guimpel, Julio Juan. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina

We report here on the preservation of ferroelectricity down to 2 nm in BiFeO3 ultrathin films. The electric polarization can be switched reversibly and is stable over several days. Our findings bring insight on the fundamental problem of ferroelectricity at low thickness and confirm the potential of BiFeO3 as a lead-free ferroelectric and multiferroic material for nanoscale devices.

The magnetic properties of a series of YBa2Cu3O7-x/La2/3Ca1/3MnO3 (YBCO/LC1/3MO) superlattices grown by dc sputtering at high oxygen pressures (3.5 mbar) show the expected ferromagnetic behaviour. However, field cooled hysteresis loops at low temperature show the unexpected existence of exchange bias, effect associated with the existence of ferromagnetic/antiferromagnetic (F/AF) interfaces. The blocking temperature (TB) is found thickness dependent and the exchange bias field (HEB) is found inversely proportional to the FM layer thickness, as expected. The presence of an AF material is probably associated to interface disorder and Mn valence shift towards Mn4+., 12 pages, 2 figures, 1 table, submitted to Applied Physics Letters

The structural and physical properties of La 0.55 Sr 0.45 MnO 3 /SrTiO 3 superlattices grown by magnetron sputtering are studied. Two deposition temperatures and different mismatched substrates and buffer layers were used. The structure was determined by refinement through X-ray diffraction pattern fitting. The results indicate 1 unit cell (u.c.) interdiffusion at the interfaces and a 1 u.c. layer thickness fluctuation, i.e. roughness. In-plane hysteresis loops show the expected ferromagnetic behavior, while the perpendicular-to-plane hysteresis loops show anomalies which could evidence magnetic domain size inhomogeneities and stress.

We studied the temperature and thickness dependence of the transport properties of La0.6Sr0.4MnO3 films. Hall voltage and magnetoresistance measurements on 10 and 150 nm thick films were performed with this porpose. From the ordinary Hall component, we calculated the density of carriers, which has hole-character and is systematically lower than that expected from the chemical composition of the manganite in both samples. Localization effects observed at low temperature in the resistivity of the thinner film, associated with the substrate-induced disorder, are correlated with a decrease of the density of carriers.

We have made a systematic study of the magnetic properties of low doped manganite films submitted to different oxygenation treatments. We have found that oxygenation dynamics depends critically of the strain field in the sample. The T C and the Mr increase as the oxygen content is increased. A decrease of the coercive field of the LSMO-STO films was observed, indicating that annealing treatments increase the oxygen content reducing oxygen vacancies.

A novel nanocomposite resist is presented based on AgNWs dispersed in poly(methyl methacrylate). It is shown that this nanocomposite resist displays sheet resistances below 10 Ω sq−1 for concentrations of AgNWs higher than and can be used for a wide range of microfabrication techniques. The resist can act as a conductive ink that cures at room temperature, form thin films with low sheet resistances, and be used in fast replication methods derived from soft lithography. Furthermore, it can be applied for nano-scale fabrication via electron beam lithography (EBL) on different substrates, including flexible and insulating materials, providing a straightforward method to avoid charging effects. This, being the first report about a nanocomposite resist based on AgNWs for EBL, describes a simple procedure to account for suspended nanowires, forming bridges, nanocantilevers and more complex nanostructures. A wide range of opportunities opens for the single-step fabrication of electronic components in the nano and micro scale.

We have studied the structure, magnetic, and transport properties of manganite-based multilayers A/Bi, with A=La0.55Sr0.45MnO3 (metallic ferromagnet), and spacers (Bi) of different nature: B1=SrTiO3 (nonmagnetic insulator), B2=La0.9Sr0.1MnO3 (insulator ferromagnet), and B3=La0.67Ca0.33MnO3 (paramagnetic-insulator/ferromagnet-metal). The samples are strongly textured in the direction perpendicular to the sample surface, and present a good interface quality with small roughness and interdiffusion. We have found that in the A/B1/A trilayers, the ferromagnetic electrodes are ferromagnetically coupled for thin spacer layers and becomes decoupled for spacer thickness larger than 3 nm. Instead, the others multilayers are ferromagnetic for all spacer thicknesses and temperature range. This result was expected for temperatures well below the spacer Curie temperature. We attributed the ferromagnetic behavior of the system, found for temperatures above the ordering temperature of the spacer, to direct exchange coupl...

International audience; Size effects and their consequences in the thermal stability of the magnetization of the micro-sized MnAs/GaAs(100) ribbons were studied by magnetic force microscopy. We found out that the orientation in which size is reduced plays a key role in the magnetic configuration and thermal stability of the micro-sized patterns. On the one hand, when reducing the size in the [0001] alpha-MnAs direction, the system shows an improvement in the thermal stability of the remanent magnetization. On the other hand, when the size is reduced in the [11-20] alpha-MnAs direction, the system goes through a magnetic reconfiguration from in-plane magnetized to out-of-plane magnetized, which also improves the thermal stability.

We have studied the transport and magnetic properties of strongly textured metal/insulator La 1− x Sr x MnO 3 ( x =0.4,0.1) bilayers and trilayers, grown by DC magnetron sputtering over MgO and SrTiO 3 substrates. The multilayers present transport properties similar to those of the La 0.6 Sr 0.4 MnO 3 films, being very sensitive to deposition conditions. Magnetic multilayers show a metal–insulator transition around T c (∼250 K) and colossal magnetoresistance which is maximum around T c . No extrinsic magnetoresistance associated with the multilayered structure was observed, probably due to the presence of ferromagnetic coupling between the metallic layers, as suggested by magnetization measurements.

The angular dependence of the magnetoresistance effect has been measured on bicrystalline La(0.75)Sr(0.25)MnO(3) films. The measurements have been performed on an electronically lithographed Wheatstone bridge. The study of the angular dependence of both the magnetoresistance and the resistance of single-crystalline and grain-boundary regions of the samples allowed us to isolate two contributions of low-field magnetoresistance in manganites. One of them is associated with the spin-orbit effect, i.e. the anisotropic magnetoresistance of ferromagnetic compounds, and the other one is related to spin-disorder regions at the grain boundary. Complementary x-ray diffraction, ferromagnetic resonance and low temperature magnetization experiments contribute to the characterization of the magnetic anisotropy of the samples and the general comprehension of the problem.

International audience; Size and orientation effects on the phase coexistence in MnAs/GaAs(001) microribbons were studied using magnetic force microscopy. The magnetostructural phase coexistence reported in MnAs thin films is also observed in the microribbons, even in the smallest ones. However, the stripe array of MnAs films is only preserved in the ribbons confined along the [0001] direction. Nevertheless, the configuration of the magnetoelastic domains is altered in the ribbons confined along the [11 (2) over bar0] direction. In this last case, the micrometric ribbons exhibit a redistribution of the magnetoelastic phases owed to the relaxation of the epitaxial strains. The results are understood in terms of the anisotropic change in the lattice parameters at the magnetostructural transition.

We have used oxygen ions irradiation to generate controlled structural disorder in thin manganite films. Conductive atomic force microscopy CAFM), transport and magnetic measurements were performed to analyze the influence of the implantation process in the physical properties of the films. CAFM images show regions with different conductivity values, probably due to the random distribution of point defect or inhomogeneous changes of the local Mn3+/4+ ratio to reduce lattice strains of the irradiated areas. The transport and magnetic properties of these systems are interpreted in this context. Metal-insulator transition can be described in the frame of a percolative model. Disorder increases the distance between conducting regions, lowering the observed TMI. Point defect disorder increases localization of the carriers due to increased disorder and locally enhanced strain field. Remarkably, even with the inhomogeneous nature of the samples, no sign of low field magnetoresistance was found. Point defect disorder decreases the system magnetization but doesn t seem to change the magnetic transition temperature. As a consequence, an important decoupling between the magnetic and the metal-insulator transition is found for ion irradiated films as opposed to the classical double exchange model scenario., Comment: 27 pages, 11 Figures

Applied Superconductivity Conference 2006, Seattle, WA, AUG 27-SEP 01, 2006; International audience; In this paper, we present several steps in the development of an HTS Giaever transformer, based on a SIS heterostructure, where both superconducting thin film should present low pinning properties and be insulated with a thin insulating layer. High Resolution AC Susceptibility measurements on YBCO//STO and NBCO//STO thin films show that the most important pinning centers are twin boundary intersections (TBI), and that their elimination with proper growth conditions allows to improve vortex mobility. When the base layer outgrowth density exceeds 10(5)/cm(2), pinholes through the insulating layer (PBCO/STO) short-circuit the electrodes. Therefore, ion beam milling at grazing incidence has been performed to reduce the height of the outgrowths otherwise protruding between 0.5 and 1.5 mu m above the surface of the film. We could reduce their density by 10 and barrier leakage by 1000 with only 10 nm of insulator thickness. Several Giaever devices were fabricated with this ion milling process and by adjusting the regrowth temperature. The influence of this new technology was investigated: AES analysis indicates a preferential erosion of copper ions, a damaged surface layer of 5 nm is deduced from RBS analysis.