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Gómez, M. E., G. Campillo, J. - G. Ramirez, A. Hoffmann, and J. Guimpel. "Detailed magnetic and structural properties of exchange-biased La1-xCaxMnO3." physica status solidi (c) 4, no. 11 (2007): 4181–4187.
Abstract: We 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). We grew FM/AF superlattices via a high-pressure sputtering technique on (001) oriented SrTiO3 substrates. We systematically varied the thickness of the ferromagnetic layers, while maintaining a fixed thickness of the antiferromagnetic layers. Alternatively, we also varied the thickness of the antiferromagnetic layers, keeping a fixed ferromagnetic layer thickness. The total superlattice thickness was kept approximately constant. XRD analysis confirms the existence of the superlattice structure by the observation of multiple satellite peaks around the (00l) manganite Bragg reflections. We extracted the average lattice parameter of the superlattice and its dependence on the thicknesses of the ferro- and antiferromagnetic layers. We conducted field cooling (FC) and zero field cooling (ZFC), magneto-thermal, and magneto-resistance measurements. The existence of an exchange bias effect at temperatures below the Néel temperature of the AF layer was revealed by magnetization loops measured after FC. We studied the dependence of magnetic parameters on the thicknesses of the ferro- and antiferromagnetic layers. We found that the structural, magnetization, and magneto transport properties as functions of F-layer thickness are all correlated. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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Gomez, M. E., G. Campillo, J. G. Ramirez, P. Prieto, A. Hoffmann, J. Guimpel, N. Haberkorn, A. Condo, and F. Lovey. "Magnetotransport properties in epitaxial exchange-biased La2/3Ca1/3MnO3/La1/3Ca2/3MnO3 superlattices." IEEE Transactions on Magnetics 42, no. 10 (2006): 2981–2983.
Abstract: Superlattices of ferromagnetic (F) and antiferromagnetic (AF) oxide materials have attracted increased attention given the exchange bias or exchange anistropy phenomenon. Research on magnetic oxide superlattices has focused toward the technological goals of increasing magnetores stance in lower applied magnetic fields and more useful temperature ranges for various applications. Superlattices of F-LCMO and AF-LCMO layers were grown on (001)-oriented SrTiO3 substrates. We studied the temperature dependence of magnetotransport properties for a series of [AF-LCMO (7.6 nm)/F-LCMO (t(F))](N) superlattices as a function of the ferromagnetically doped layer thickness, t(F), while the antiferromagnetic (AF) layer thickness, t(AF), was kept constant. Magnetotransport measurements at different temperatures were done on a series of [AF(7.6 nm)IF(t(F))](N) superlattices. The ZFC resistance has a maximum at negative fields, for all multilayers, with descending fields (from 1 to -1 kOe). In all samples a shift along the field axis of the FC loop with respect to that of the ZFC loop is observed. The H-ex values determined from these displacements of the FC loops of the magnetoresistance loops increase when temperature decreases and its magnitude also depends on the ferromagnetic layer thickness.
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Hoffmann, A., G. Nieva, J. Guimpel, Y. Bruynseraede, J. Santamaria, D. Lederman, and I. K. Schuller. "Comment on “Photoemission study of YBa2Cu3Oy thin films under light illumination”." PHYSICAL REVIEW LETTERS 97, no. 11 (2006): 119701.
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