Magneto-transport characteristics of La1.4Ca1.6Mn2O7 thin film deposited by spray pyrolysis

Polycrystalline thin films of double layer manganite La1.4Ca1.6Mn2O7 (DLCMO) have been deposited by nebulized spray pyrolysis on single crystal LaAlO3 substrates. These single phase films, having grain size in the range ∼70–100 nm, exhibit a ferromagnetic transition (FM) at TC ∼ 95 K. The short range FM ordering due to the in-plane spin coherence is shown to occur at a higher temperature around ∼125 K. The metal to insulator transition occurs at a lower temperature TP ∼ 55 K. The transport mechanism above TC is of Mott's variable range hopping type. Below TC the current–voltage characteristics show non-linear behaviour that becomes stronger with decreasing temperature. At lower temperatures below TCA ∼ 50 K, a magnetically frustrated spin glass-like state is known to exist. The DLCMO films exhibit reasonable low field magneto-resistance of ∼5% at 0.6 kOe and ∼13% at 3 kOe at ∼77 K. This has been explained on the basis of complete spin-polarized tunnelling of charge carriers through the insulating (La, Ca)O2 layers between the adjacent MnO2 bilayers.