Magnetotransport properties, electronic structure, and microstructure of La_0.7 Sn_0.3 Mn O₃ thin films

Single-phase La0.7 Sn0.3 Mn O3 (LSnMO) thin films were fabricated on LaAl O3 (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 K. The x-ray absorption spectroscopy (XAS) of the as-deposited LSnMO films shows signature of Mn3+/Mn2+ mixed valence indicating that tetravalent Sn ions may have resulted in electron doping into the eg 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 La1-x Snx Mn O3 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 La1-x Mn O3 phases.