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Register a new userSubstrate-induced strain effects on Pr_{0.6}Ca_{0.4}MnO_{3} films
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We report the characterization of the crystal structure, low-temperature charge and orbital ordering, transport, and magnetization of Pr_{0.6}Ca_{0.4}MnO_{3} films grown on LaAlO_{3}, NdGaO_{3}, and SrTiO_{3} substrates, which provide compressive (LaAlO_{3}) and tensile (NdGaO_{3} and SrTiO_{3}) strain. The films are observed to exhibit different crystallographic symmetries than the bulk material, and the low-temperature ordering is found to be more robust under compressive-- as opposed to tensile-- strain. In fact, bulk-like charge and orbital ordering is not observed in the film grown on NdGaO_{3}, which is the substrate that provides the least amount of nominal and measured, but tensile, strain. This result suggests the importance of the role played by the Mn--O--Mn bond angles in the formation of charge and orbital ordering at low temperatures. Finally, in the film grown on LaAlO_{3}, a connection between the lattice distortion associated with orbital ordering and the onset of antiferromagnetism is reported.
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We report the detailed study of dielectric response of Pr(0.6)Ca(0.4)MnO(3) (PCMO), member of manganite family showing colossal magnetoresistance. Measurements have been performed on four polycrystalline samples and four single crystals, allowing us to compare and extract the essence of dielectric response in the material. High frequency dielectric function is found to be 30, as expected for the perovskite material. Dielectric relaxation is found in frequency window of 20Hz-1MHz at temperatures of 50-200K that yields to colossal low-frequency dielectric function, i.e. static dielectric constant. Static dielectric constant is always colossal, but varies considerably in different samples from 1000 until 100000. The measured data can be simulated very well by blocking (surface barrier) capacitance in series with sample resistance. This indicates that the large dielectric constant in PCMO arises from the Schottky barriers at electrical contacts. Measurements in magnetic field and with d.c. bias support this interpretation. Weak anomaly at the charge ordering temperature can also be attributed to interplay of sample and contact resistance. We comment our results in the framework of related studies by other groups.
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