Substrate-Induced Anomalous Electrical Transport and Magnetic Transitions in Epitaxial La 0.66 Sr 0.33 MnO 3 Films Grown
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Mat. Res. Soc. Symp. Proc. Vol. 602 © 2000 Materials Research Society
EXPERIMENTAL DETAILS We have grown 500/A La0.66Sr0.33MnO3 epitaxial films on (001) BTO substrate by 900 off-axis rf-magnetron sputtering using a 2 in. diameter stoichiometric target. A if (13.56 MHz) power of 100 W was applied. The process was carried out in a flowing gas mixture of argon with oxygen in the 12 : 8 volumetric ratio with 200 mTorr total partial pressure. The growth temperature for the substrate was optimized at 7500 C. After deposition the films were cooled under ambient oxygen of 300 Torr. The in-plane and out-of-plane lattice parameters and the associated 3D strain states in the films were determined by normal and grazing incidence diffraction (GID) using a four-circle x-ray diffractometer with Cu Kax radiation. The bulk LSMO target has a pseudocubic perovskite structure with lattice parameters a -" 3.884 Ak.The tilting of MnO 6 octahedra results in a rhombohedral structure with a relation a~hom = '/2ap and a•= 600 .The pseudocubic lattice parameters are rotated 450 from the rhombohedral lattice parameters (a~hom). In this paper we will
describe the Miller indices of the LSMO planes based on pseudocubic perovskite unit cell structure. The temperature-dependent electrical and magneto transport measurements were carried out using a 4-point DC technique employing Oxford Instruments' MagLab System 2000TM. Magnetic measurements were carried out using a Quantum Design superconducting quantum inteiference device (SQUID) magnetometer. Special sample holders were used to position the samples along chosen crystallographic directions. RESULTS The LSMO films are grown on (001) BTO substrate. At film deposition temperature the substrate is in cubic phase. At room tem~perature in tetragonal phase, the a-axis and c-axis lattice parameters of BTO substrate are 3.997 A and 4.037 A (c/a =1.01), respectively. After a thermal cycle through the film growth temperature the single domain BTO substrate becomes a mixture of two different kind of domains of (001) (-60%) and (100) (-40%) normal orientations. The lattice mismatch (+2.9 %) between film and substrate induces in-plane biaxial tensile stress in the LSMO films. Figure 1 shows the normal 0- 26 x-ray diffraction scan of 500 A•LSMO film on BTO 106 105
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Fig. 1. X-ray normal 0 -20
LSMO
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3.997 A
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scans for 500 A LSMO BaTiO3 substrates. The dotted line indicate bulk 20 value of LSMO. Inset shows the schematic diagrams of crosssectional view of the strained lattice.
101 • 26 substrate. The out-of-plane pseudocubic lattice spacing (d001) of the film is obtained to be (3.841±+0.001) A. The in-plane lattice spacing of the film from grazing incidence x-ray diffraction
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(GID) is found to be (3.942_+0.006) A. This indicates that the 500 A LSMO film grown on BTO has an in-plane biaxial tensile strain with Ex= 6yy = + 1.5 % and a corresponding out-of-plane uniaxial compression with Ez= -1.1 %. The film is no
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