Metastable resistivity of La0.8Ca0.2MnO3 manganite thin films

Transport properties of La0.8Ca0.2MnO3 thin films 15 and 130 nm thick have been investigated and confronted with the properties of bulk single crystals of the same composition. It has been found that low-temperature resistivity of the films is sensitive to electric current and/or field treatment and thermal history of the sample. Thin films exhibit a variety of metastable resistive states and spontaneously evolve toward high-resistivity state in which the films exhibit highly nonlinear transport behavior at low temperatures. Nonlinear V-I characteristics are well described by indirect tunneling model. The memory of the resistivity can be, at least partly, erased by a heat treatment at temperatures above the memory erasing temperature. The memory erasing temperature for thin films, T=450 K, is significantly higher than that of single crystals. The results are interpreted in the context of strain driven phase separation. Coexistence of two ferromagnetic phases with different orbital orders and different conductivities is influenced by strains due to thermal cycling and current flow.