The preparation, crystallization and analysis of colossal magnetoresistive materials using the deposition by aqueous acetate solution technique.

摘要

Manganese based perovskites are being investigated because of their potential uses in actuators, sensors, magnetoresistive random access memory (MRAM), and magnetic recording heads. The operation of these devices relies on the simplistic principle of magnetoresistance, in which the resistivity of a device changes with the application of a magnetic field. Colossal magnetoresistance (CMR) is a fairly recent development in which the device operation results from the extremely large changes in resistance, exhibited by applied magnetic fields. The usefulness of the phenomenon has been hampered by two factors: (1) the low temperature of occurrence, and (2) the magnitude of required magnetic fields. Today, the term colossal magnetoresistive materials is typically associated with the doped manganites existing in the perovskite crystalline structure.; The manganese based perovskites are successfully synthesized in our laboratory by the Deposition by Aqueous Acetate Solution (DAAS) technique. Described will be an approach aimed at synthesizing manganite materials using the DAAS technique to produce powdered samples which are easily analyzed, as well as the production of the technologically required thin films. The alternate use of A and B-Site doping is used to attend magnetoresistance at ambient temperatures. Further, the chemistry of the DAAS technique will be illustrated with thermogravimetric analysis and Fourier Transform Infrared Spectroscopy. The crystalline structure of the perovskites has been analyzed with X-ray diffraction during the temperature dependent periods of growth, and the resulting resistivities will be shown. Finally, we describe a new approach in which Transmission FTIR analysis is used to determine the metal-insulator transition temperature (T_MI) of the manganese based perovskites. The FTIR transmission signal is shown to be associated with the imaginary part of the dielectric function (i.e., correlating to the dielectric loss) of the perovskites, and exhibits a large change in transmittance at temperatures corresponding to the highest values of resistance. The effect of temperature on the FTIR spectral shift, and change in band intensity at 590 cm−1 (i.e., the metal-oxygen vibration in the MnO₆ octahedra) is used to infer the degree of electron-phonon interactions in the manganese based perovskites.