Local Crystal Structure Modifications in Pulsed Laser Deposited Colossal Magnetoresistive Oxide Thin Films
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Local Crystal Structure Modifications in Pulsed Laser Deposited Colossal Magnetoresistive Oxide Thin Films M. Alper Sahiner1, Wiqar Shah1, Marc Aranguren1, Jeffrey Serfass1, Joseph C. Woicik2 1
Seton Hall University, Physics Department, South Orange, New Jersey 07079 National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA 2
ABSTRACT The local structure around the manganese atom is probed by extended x-ray absorption spectroscopy (EXAFS) measurements in pulsed laser deposited thin films of La1-xCaxMnO3 (x=0.12-0.53). The thin films were deposited on various single crystal oxide substrates. The effect of the lattice parameter of the substrate on the local structural modifications around Mn atom is investigated. All the x-ray absorption experiments were performed at the National Synchrotron Light Source of Brookhaven National Laboratory. By detailed EXAFS theoretical modeling for the possible local structures and the least square fitting to the EXAFS data using these models, the overall substrate and the Ca concentration effects are probed. The EXAFS results indicate a rigid Mn-O bonding, but response of the Mn-O-Mn bond angle upon variations of the substrate lattice constant and Ca substitution. INTRODUCTION La1-xCaxMnO3 has attracted considerable interest because of their exhibition of colossal magnetoresistance (CMR) effect. Since electron-lattice coupling is considered to be an important factor in observance of the CMR effect in these materials, detailed information on the local arrangements of atoms is in particular interest. Modifications over the local structure could be introduced either by Ca substitution for La or substrate induced effects for thin films of these materials. The substrate induced compressive or tensile stresses can modify the lattice parameters of the thin films of these materials thus could have an important effect on the magnetoresistive properties. In this work, we deposited a series of thin films of La1-xCaxMnO3 on various oxide substrates in order to introduce different stresses on the films. The local structure around the Mn atoms is probed by x-ray absorption spectroscopy. Previously, substrate effects on the structure and the magnetic properties on similar systems were investigated by x-ray diffraction and x-ray absorption spectroscopy [1, 2]. The structural variations upon Ca substitution were studied for bulk La1-xCaxMnO3 polycrystalline samples [3]. La1-xCaxMnO3 exhibits ferromagnetic behavior for 0.2 < x 0.5 and CMR effect around x = 0.33. In this study, our goal was to systematically study the thin films of La1-xCaxMnO3 around these x values and for various substrates. EXAFS being very sensitive to local modifications around the main absorbing atom (Mn atom in this study) can reveal subtle structural variations caused by either substrate variations or Ca substitution. The detailed analyses of the EXAFS data were performed
in the light of EXAFS calculations by using University of Washington’s multiple scattering EXAFS simulation code FEFF8
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