Magnetotransport properties, electronic structure, and microstructure ofLa0.7Sn0.3MnO3thin films

Abstract

Single-phase ${\mathrm{La}}_{0.7}{\mathrm{Sn}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$ (LSnMO) thin films were fabricated on $\mathrm{La}\mathrm{Al}{\mathrm{O}}_{3}$ (LAO) substrates by pulsed laser deposition (PLD). The as-deposited films, though showed insulating characteristics with no sign of insulator-metal transition (IMT) down to very low temperatures, did display a paramagnetic-ferromagnetic transition (PFT) around $180\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The x-ray absorption spectroscopy (XAS) of the as-deposited LSnMO films shows signature of ${\mathrm{Mn}}^{3+}∕{\mathrm{Mn}}^{2+}$ mixed valence indicating that tetravalent Sn ions may have resulted in electron doping into the ${e}_{\mathrm{g}}$ band of Mn. The transmission electron microscopy (TEM) analyses on the as-deposited LSnMO films further confirmed that the films are epitaxial with uniform composition distributions. It is suggestive that the doping level of $x=0.3$ in ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sn}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$ can be achieved without disrupting the perovskite structure or any composition inhomogeneity. On the other hand, ex situ annealing in oxygen as well as in argon atmosphere, though both drive the films to display IMT and a marked enhancement in the transition temperature, the preservation of LSnMO phase is somewhat doubtful. In the oxygen-annealing case, the evidence from the XAS measurements on Sn ions though showed the existence of tetravalent characteristics, the Hall measurements indicated that the obtained LSnMO films are $p$ type in nature. Furthermore, the TEM analyses also revealed the emergence of the Sn compounds, which may ultimately drive the obtained films into La-deficient ${\mathrm{La}}_{1\ensuremath{-}x}\mathrm{Mn}{\mathrm{O}}_{3}$ phases.