We report here on an experimental study of slow thermal relaxation effects from the metastable metallicferromagnetic phase to the insulating one in a charge-ordered manganese oxide, Pr 0.67 Ca 0.33 MnO 3 . The metalinsulator transition is evidenced by an abrupt jump of the resistivity by several orders of magnitude at a well-defined time while there is no apparent singularity in the magnetization relaxation. This supports the view of a percolative behavior of current transport. The magnetic relaxation is discussed in terms of a two-level phenomenological model with a distribution of energy barriers.
We present the monovalent alkali metal substitution effects upon structural, magnetic and electrical properties in La 0.7 Sr 0.3−x Na x MnO 3 for 0 x 0.2. X-ray diffraction patterns show that our powder samples crystallize in a rhombohedral distorted perovskite structure with R 3c space group. All the samples exhibit a ferromagnetic-paramagnetic transition and metallicsemi-conductor one with increasing temperature. The Curie temperature T C decreases from 365 to 305 K; however the resistivity transition temperature T ρ decreases from 340 to 270 K as Na content increases. A magnetoresistance ratio of about 46% at 300 K and in an applied field of 10 T has been observed in the bulk ceramic La 0.7 Sr 0.1 Na 0.2 MnO 3 sample.
We have synthesized (Sm1−x,Cax)MnO3 and related compositions to show their potential use as thermochromic switch in the infrared range. Depending on temperature or composition, the single phase is stabilized using the polyacrilamide gel process. Infrared transmittance was measured on selected samples in the 1,42–25μm range. Relative contrast up to 0.773 is measured in the 8–14μm range. Full opacity in the 8–14μm range occurs at temperatures between 273 and 300K, depending on the composition. The potential application of perovskites manganites as thermochromic infrared switch or coating is discussed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.