Structure Microstructure

The influence of the substrate upon the microstructure/structure, the lattice parameters, the texturation, and also the orientation of the film is discussed in this section.

Using magnetic force microscopy, Kwon et al. [87] showed on La0

7Sr0.3MnO3 a "featherlike" ^Ite!^ indicating an in-plane magnetization on (100)-SrTiO3, while on (100)-LaAlO3, a "mazelike" pattern corresponding to a perpendicular magnetization anisotropy is seen. This kind of study was confirmed and extended recently by Desfeux et al. on other substrates [106].

The influence of the substrate can principally be deduced from the lattice parameters of the film and the effect of strain on lattice parameters has been studied by many groups. These measurements lead to different spin structures. This is evident in La1-XSrxMnO3 for which the spin-orbital phase diagram was obtained in the plane of strain-field (c/a ratio) vs doping x using the density-functional electronic calculation [107]. The phase diagram of La0.67Sr0.33MnO3 was also plotted for different substrates [108]. A strong dependence of anisotropy and Curie temperature on lattice strain is observed. The effect of uniaxial strain was studied theoretically by Ahn et al. [109]. Uniaxial strain produces changes in the magnetic ground state, leading to dramatic changes in the band structure and optical spectrum.

Both in-plane and out-of-plane lattice parameters are often modified by stain effects when various substrates are used [110]. In Figure 10, the 0-20 scan shows that the Pr0.5Ca0.5MnO3 films are single phase and highly crystallized, as seen from the sharp and intense diffraction peaks. It is also found that the films were [010]-oriented (i.e., with the [010] axis perpendicular to the substrate plane) on the STO substrate and [101]-oriented on LAO. Using the X-ray diffraction (XRD) results, the out-of-plane lattice parameter of the substrates was calculated to be 0.3778 nm for STO and 0.3834 nm for LAO. This confirms that the films are under tensile stress on STO (decreasing in the growth direction and expanding in the plane) and under compressive stress on LAO (decreasing in the plane and expanding in the out-of-plane direction) due to the lattice mismatch between the film and the substrate at room temperature (Fig. 11). The strain effects on the out-of-plane lattice parameter of LCMO are enhanced with annealing [111]: the lattice expansion is 2-3 times larger in LCMO/STO than in LCMO/NGO. The stress also influences the bond lengths and bond angles. Miniotas et al. have evaluated the Mn-O and Mn-Mn distances in La1-x Cax MnO3 films grown by MBE. The Mn-O bond length was found to be fixed at 0.1975 nm, independent of the substrate types, while the Mn-Mn distance (and

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