Haberkorn, N., J. Guimpel, M. Sirena, L. B. Steren, G. Campillo, W. Saldarriaga, and M. E. Gomez. "Interface disorder and transport properties in HTC/CMR superlattices." PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 408 (2004): 896–897.
Abstract: The physical properties of superlattices are affected by interface disorder, like roughness and interdiffusion. X-ray diffraction allows its measurement through modeling and structure refinement. The high-T-c RBa2Cu3O7 (RBCO) and colossal magneto resistance La(x)A(1-x)MnO(3) (LAMO) perovskites are interesting superlattice partners given their similar lattice parameters and because the combination of magnetic and superconducting properties is interesting for both basic and applied research. We have investigated the structural and transport properties of YBCO/La2/3Ca1/3MnO3 and GdBCO/La0.6Sr0.04MnO3 superlattices grown by sputtering on (100)MgO. We find a roughness of 1 RBCO unit cell and a 30% interdiffusion in the same length from the interfaces for all samples. The superconducting behavior is found strongly dependent on the LAMO layer thickness. (C) 2004 Elsevier B.V. All rights reserved.
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Sirena, M., N. Haberkorn, M. Granada, L. B. Steren, and J. Guimpel. "Oxygen and disorder effect in the magnetic properties of manganite films." JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 272 (2004): 1171–1173.
Abstract: 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. (C) 2004 Elsevier B.V. All rights reserved.
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Haberkorn, N., M. Sirena, J. Guimpel, and L. B. Steren. "Disorder influence on the magnetic properties of La0.55Sr0.45MnO3/SrTiO3 superlattices." JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 272 (2004): 1244–1246.
Abstract: The structural and physical properties of La0.55Sr0.45MnO3/SrTiO3 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. (C) 2004 Elsevier B.V. All rights reserved.
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Granada, M., B. Maiorov, M. Sirena, L. B. Steren, and J. Guimpel. "Hall effect in La0.6Sr0.4MnO3 thin films." JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 272 (2004): 1836–1838.
Abstract: 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. (C) 2003 Elsevier B.V. All rights reserved.
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Haberkorn, N., J. Guimpel, M. Sirena, L. B. Steren, W. Saldarriaga, E. Baca, and M. E. Gomez. "Antiferromagnetism at the YBa2Cu3O7/La2/3Ca1/3MnO3 interface." Applied Physics Letters 84, no. 19 (2004): 3927–3929.
Abstract: 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 behavior. However, field-cooled hysteresis loops at a low temperatures show the unexpected existence of exchange bias effect associated with the existence of ferromagnetic/antiferromagnetic (AF) interfaces. The blocking temperature (T-B) is found to be thickness dependent and the exchange bias field (H-EB) is found to be inversely proportional to the ferromagnetic layer thickness, as expected. The presence of an AF material is probably associated with interface disorder and Mn valence shift toward Mn4+. (C) 2004 American Institute of Physics.
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Guimpel, J., N. Haberkorn, M. Sirena, L. B. Steren, W. Saldarriaga, E. Baca, and M. E. Gomez. "Interface effects in perovskite superlattices." JOURNAL OF LOW TEMPERATURE PHYSICS 135, no. 1-2 (2004): 115–118.
Abstract: The effect of interface disorder in perovskite superlattices, either with the substrate or between layers dominates the physics of the material, even when the lattice parameter of the component materials differs in less than 1%. Unexpected behavior emerges, like exchange bias in a system where no antiferromagnetic material has been included in the superlattice design.
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Sirena, M., N. Haberkorn, M. Granada, L. B. Steren, and J. Guimpel. "Oxygen and disorder effect in the magnetic properties of manganite films." Journal of Magnetism and Magnetic Materials 272-276, Part 2 (2004): 1171–1173.
Abstract: 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 TC 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.
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Sirena, M., N. Haberkorn, M. Granada, L. B. Steren, and J. Guimpel. "Metal-insulator transition induced by postdeposition annealing in low doped manganite films." JOURNAL OF APPLIED PHYSICS 105, no. 3 (2009).
Abstract: We studied the transport and magnetic properties of low-doped manganite films after different oxygenation processes. The oxygen content was adjusted by postdeposition annealing at different oxygen pressures and annealing times. For all the samples we observed an increase in the Curie temperature and the remnant magnetization with the oxygen content. In general, for decreasing number of oxygen vacancies, samples under expansive strain become more homogeneous and their electrical resistivity decreases. A metal-insulator transition is induced in highly oxygenated films grown on SrTiO3, probably related to a shift of the mobility edge crossing below the Fermi energy. We found that the oxygenation dynamics depend critically on the strain field induced by the substrates and also on the Sr doping concentration.
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Sirena, M., A. Zimmers, N. Haberkorn, E. E. Kaul, L. B. Steren, J. Lesueur, T. Wolf, Y. Le Gall, J. - J. Grob, and G. Faini. "Direct observation of electronic inhomogeneities induced by point defect disorder in manganite films." Journal of Applied Physics 107 (2010): 113903.
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Sirena, M., E. Kaul, M. B. Pedreros, C. A. Rodriguez, J. Guimpel, and L. B. Steren. "Structural, magnetic and electrical properties of ferromagnetic/ferroelectric multilayers." Journal of Applied Physics 109, no. 12 (2011): 123920.
Abstract: The La0.75Sr0.25MnO3 (LSMO)/Ba0.7Sr0.3TiO3 (BSTO) superlattices and bilayers, where LSMO is ferromagnetic and BSTO is ferroelectric, were grown by dc sputtering. X-ray diffraction indicates that the samples present a textured growth with the c axis perpendicular to the substrate. Magnetization measurements show a decrease of the sample’s magnetization for decreasing ferromagnetic thickness. This effect could be related to the presence of biaxial strain and a magnetic dead layer in the samples. Conductive atomic force microscopy indicates that the samples present a total covering of the ferromagnetic layer for a ferroelectric thickness higher than four unit cells. Transport tunneling of the carriers seems to be the preferred conduction mechanism through the ferroelectric layer. These are promising results for the development of multiferroic tunnel junctions.
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