Following the lack of microscopic information about the intriguing well-known electrical-thermal switching mechanism in carbon-black-polymer composites, we applied atomic force microscopy in order to reveal the local nature of the process and correlated it with the characteristics of the widely used commercial switches. We conclude that the switching events take place in critical interparticle tunneling junctions that carry most of the current. The macroscopic switched state is then a result of a dynamic-stationary state of fast switching and slow reconnection of the corresponding junctions.
We report structural, electrical, thermopower and magnetic properties of the Ru 1−x Co x Sr 2 Eu 1.5 Ce 0.5 Cu 2 O 10−δ (1.0 x 0.0) system. Substitution of Co at the Ru site in the Ru 1−x Co x Sr 2 Eu 1.5 Ce 0.5 Cu 2 O 10−δ system takes place iso-structurally in the tetragonal structure (space group I 4/mmm) with full solubility (x = 1.0). Superconductivity (SC) exists for x up to x = 0.075 only and at higher Co concentrations SC is totally suppressed. The magnetic behaviour of the materials with Co up to x = 0.2 preserves the magnetic structure of the parent RuSr 2 Eu 1.5 Ce 0.5 Cu 2 O 10−δ compound. For 0.8 x 0.2 an antiferromagnetic-like transition is seen at T N = 31 K, which remains invariant regardless of the Co content. CoSr 2 Eu 1.5 Ce 0.5 Cu 2 O 10−δ (x = 1) seems to be an itinerant magnet, which orders magnetically at around 110 K, though for such an assertion further work is warranted. In general, the magnetization measurements as such did not reveal the complete information on the magnetic structure and hence the neutron scattering measurements are still required to resolve the complex magnetism of Ru 1−x Co x Sr 2 Eu 1.5 Ce 0.5 Cu 2 O 10−δ and even the pristine system.
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