Creation and annihilation of conducting filaments in mesoscopic manganite structures

Anomalous transport properties are observed in mesoscopic (several hundreds of nanometers to several micrometers) structures of manganite Pr-0.65(Ca0.75Sr0.25)(0.35)MnO3: (i) spontaneous jumps of resistance occur during both the ramping of magnetic field and the relaxation after the field cycle; and (ii) in certain ranges of temperature and magnetic field, steplike negative differential resistance (NDR) emerges in the current vs voltage measurements as the bias voltage reaches critical values. Two elements are responsible for the appearance of these giant sharp resistive steps: (i) a field- and temperature-dependent mixture of ferromagnetic metallic (FMM) and charge-ordered insulating (COI) phases found in this material; (ii) similarity between device dimensions and the size of competing FMM and COI domains. The phenomenology of the observed spontaneous steps is consistent with the filamentary conduction that has been previously observed in these materials with multiphase coexistence. The switching of individual conducting filaments manifests themselves as the discrete resistance steps in the mesoscopic samples while its effect is much less visible in continuous films. A local Joule heating-induced annihilation of conducting filaments is proposed as the underlying mechanism for the NDR.