Inverse thermal hysteresis and peculiar transport properties of La _0.9MnO_3-δ film

Magnetic and transport properties of 100 nm thick La_0.9MnO _3-δ manganite films have been studied in the temperature range 5 - 300 K. The films exhibit a paramagnetic to ferromagnetic transition at T_C ≈ 194 K. The temperature dependence of the resistivity shows a metal-insulator transition at 204 K and a strong resistivity increase at temperatures T < 160 K. Variations of resistivity with magnetic field and current are non-hysteretic, while the temperature dependence of the resistivity exhibits unusual inverse thermal hysteresis. The magnetic field independent inverse thermal hysteresis depends significantly on the thermal history of the sample. The data suggests that nonlinear transport characteristics are attributed to inelastic tunneling through intrinsic tunnel juctions formed by phase separated ferromagnetic metallic domains and insulating antiferromagnetic matrics.