TiO2 thin films for spintronics application: a Raman study

We present the results of a systematic study performed by micro-Raman spectroscopy on pure anatase, pure rutile and mixed anatase-rutile TiO2 thin films, deposited by radio frequency magnetron sputtering on quartz substrates, with different thicknesses. The crystal structures of the as-deposited films were unambiguously determined and a good crystalline homogeneity was revealed by a systematic mapping of the samples. In the mixed-phase films, the relative amount of the two phases was monitored by a simple analysis of the components of the multi-Lorentzian fitting curves. For the single-phase films, the influence of the thickness and the effect of different thermal treatments, carried out to obtain series of thin films differing only for oxygen content, are discussed. The analysis of the scattered light has provided indication about the presence of an interface layer between the substrate and the film, which can play a role in driving the interesting magnetic properties exhibited by our samples, which are of potential usefulness for spintronics application. The results obtained from other techniques are briefly reported and discussed in relation to our systematic Raman characterization. This study points out how Raman investigation can provide suggestions toward the understanding of the complex physical phenomena leading to room-temperature ferromagnetism in TiO2 thin films.