Conclusion

The structural, magnetic, and transport properties of man-ganite thin films have been presented in this chapter. As seen, the colossal magnetoresistive oxides display an exciting diversity of behavior in the form of thin films, and an extremely large amount of work has been carried out on thin films showing the great potential of their magnetic and transport properties. It has been shown that the structural and physical properties of these oxides are strongly dependent on the deposition procedure, chemical composition, and applied strain. For this reason, the direct comparison of data between a thin film and a bulk material (ceramic or single crystal) is difficult due to the stress in the thin film.

It has also been shown that devices are interesting and potentially useful for magnetic sensors. Prior to the fabrication of such devices, it will be necessary to characterize the materials more comprehensively, in particular from the view point of the structure and the microstructure. This is clearly evidenced by the fact that intrinsic phenomena such as the substrate-induced strain and the thickness dependence, which are directly related to the thin film process, strongly affect the magnetotransport properties. These results suggest that the local lattice distortions of the Mn-O bonds in the manganite thin films contribute to changes in the physical properties.

There are two main ideas that should be considered in the future based on the recent results. It is now recognized that the strains directly affect the lattice parameters. In addition, researchers have noted that there is a clear relation between the oxygen content (or indirectly the Mn3+/Mn4+ ratio) and the lattice parameters of the unit cell of the film. Thus, one should ask the following question: what is the relation between the oxygen content and strain? This triangular connection must be investigated precisely and explained in the future. The second main direction is related to the stress, because despite the large amount of work published on manganite thin films, there is still no direct proof of substrate-induced strains: researchers have only found indirect correlations at room temperature. More sophisticated mechanisms going beyond classical concepts (i.e., by looking at the evolution of the structure under cooling) and theoretical work, in particular by quantifying the stress for these oxide films, are required to understand the nature of this class of compounds.

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