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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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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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Prieto, P., M. E. Gomez, G. Campillo, A. Berger, E. Baca, R. Escudero, F. Morales, J. Guimpel, and N. Haberkorn. "Exchange-coupling effect and magnetotransport properties in epitaxial La2/3Ca1/3MnO3/La1/3Ca2/3MnO3 superlattices." PHYSICA STATUS SOLIDI A-APPLIED RESEARCH 201, no. 10 (2004): 2343–2346.
Abstract: We have measured structural, magnetic and, magneto transport properties of heterostructures consisting of La1-xCaxMnO3 ferromagnetic (FM) layers (x = 0.33) and antiferromagnetic (AF) layers (x = 0.67). FM/AF superlattices were grown by a high-pressure sputtering technique on (001) oriented SrTiO3 substrates. We have systematically varied the thickness of the ferromagnetic layers, while maintaining the thickness of the antiferromagnetic layers fixed. The total superlattice thickness was held approximately constant. The XRD analysis confirmed the existence of the superlattice structure by the multiple satellite peaks around the 001 manganite Bragg reflections. We have done field cooling (FC) and zero field cooling (ZFC) magnetization, and magneto resistance measurements at temperatures between 10 K and 280 K. The existence of an exchange bias effect at temperatures below the Neel temperature of the AF layer was revealed by magnetization loops after field cooling. The exchange bias field magnitude H-ex exhibited exponential temperature dependence below the blocking temperature, as well as an inverse proportionality with the ferromagnetic layer thickness. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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