The magneto-transport properties of epitaxial La_0.7Sn _0.3MnO₃ manganite thin films

Single-phase La_0.7Sn_0.3MnO₃ (LSnMO) thin films were fabricated on SrTiO₃ (STO) substrates by pulsed laser deposition (PLD). The as-deposited films, though were insulating with no sign of insulator - metal transition (IMT), did display paramagnetic-ferromagnetic transition (PFT) around 150 K. Ex situ annealing of the films at 850 °C in 250 Torr oxygen for 4 h, nonetheless, not only significantly improves the crystallographic quality but also raises IMT and PFT at 315 K and 320 K, respectively. The manifestations of spin-glass-like behavior in both the as-deposited and post-annealed films suggest that it could be intrinsic LSnMO, albeit transport properties can be drastically changed by the strain originating from large ion-size misfit between Sn and La and film/substrate epitaxial relation. The preliminary X-ray absorption spectroscopy shows signature of Mn³⁺/Mn²⁺ mixed-valence indicating that tetravalent Sn ions does result in electron-doping into the eg band of Mn.