Preparation and properties of La1 − xAgyMnO3 + δ thin epitaxial films

We report here the preparation and properties of La1 − xAgyMnO3 + δ thin epitaxial films. The original two-step preparation procedure was developed. At first, La1 − xMnO3 + δ were grown epitaxially by metal–organic chemical vapor deposition on the single-crystal substrates (001) and (110) SrTiO3, (001) LaAlO3, (111) and (001) ZrO2(Y2O3). Treatment by the vapor of the metallic silver in the oxygen atmosphere (at 1 bar and 20 bar) was the second step resulting in the selective absorption of silver by La1 − xMnO3 + δ phase. The value of y depended on the process conditions and revealed different kinetics of the silver absorption for (001) and (110) orientation of La1 − xMnO3 + δ films. The films prepared were characterized by X-ray diffraction, scanning electron microscopy with energy-dispersion X-ray analysis, high resolution transmission electron microscopy, X-ray photoelectron spectroscopy, electrical resistivity and magnetoresistance measurements in a four-probe configuration. We have found that metal-insulator transition temperature (Tp) in the series La1 − xAgxMnO3 + δ possessed a maximum of 380 K at x = 0.15. Thus, Tp of La1 − xAgxMnO3 + δ films was significantly higher than ever reported in the literature for the La1 − xAgxMnO3 + δ ceramics. La1 − xAgxMnO3 + δ films demonstrated the important role of the ferromagnetic fluctuations above Curie temperature Tc resulting in the sign change of the resistivity curve temperature slope dR / dT and a significant shift of Tp well above Tc. The maximum of the magnetoresistance on the temperature scale was close to dR / dT maximum. The intrinsic magnetoresistance values as high as 22% at 310 K and 50% at 280 K were measured in the magnetic field of 1 T in the series of La1 − xAgyMnO3 + δ epitaxial films.