Intrinsic metastability of low doped manganites: La<Subscript>0.8</Subscript>Ca<Subscript>0.2</Subscript>MnO<Subscript>3</Subscript> case

Transport properties of phase separated La<Subscript>0.8</Subscript>Ca<Subscript>0.2</Subscript>MnO<Subscript>3</S ubscript> crystals in the aged highly resistive metastable state were studied. It was found that the coexistence of different ferromagnetic phases at low temperatures is sensitive to electric current/field. In a contrast with the previously studied low resistivity metastable states the high resistivity state exhibits positive magnetoresistance and significant current dependence of the resistivity even at temperatures much higher than the Curie temperature. Application of current pulses results in appearance of zero bias anomaly in the current dependent conductivity. Similarly to the low resistivity metastable states the memory of the resistivity can be erased only after heating of the sample to T<Subscript>e</Subscript> ≈360 K. After one year storage at room temperature the La<Subscript>0.8</Subscript>Ca<Subscript>0.2</Subscript>MnO<Subscript>3</S ubscript> samples show clear signatures of aging. The aged samples spontaneously evolute towards high resistivity states. The results are discussed in the context of a coexistence of two ferromagnetic phases with different orbital order and different conductivity. The metallic ferromagnetic phase seems to be less stable giving rise to the experimentally observed electric field effects and aging. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2005