Degradation of LaMnO{3-y} surface layer in LaMnO{3-y}/ metal interface

We report electrical measurements showing the degradation processes of LaMnO$_{3-y}$ (LaMnO) in LaMnO/normal metal interface in both point contact and planar-type junctions. Immediately after the preparation of the interface, the degradation process was followed by measuring the evolution of the junction resistance versus time. This process is characterized by the appearance of a second maximum in the resistance vs. temperature (R-T) dependence at temperatures lower than the Curie temperature T$_c$, at which the metal-insulator transition occurs in the bulk. These effects are explained in terms of the formation of a depleted interface layer in LaMnO caused by an out-diffusion of oxygen from the manganite surface to the normal metal. This assumption is confirmed by XPS measurement. Similar results on LaSrMnO$_{3-y}$ interfaces are also obtained.Comment: 4 pages, 3 figures, accepted for publication in Appl. Phys. Lett.(2002

Growth of magnetoresistant La1-xMnO3 films on r-plane cut sapphire

We have prepared thin La1-xMnO3 films on r-plane cut sapphire by liquid source MOCVD. Tetramethylheptadionates of La and Mn (La(thd)3 and Mn(thd)3) were used as precursors and diethyleneglycol dimethyl ether as a solvent. The films were grown at deposition temperature TD = 800 °C . Temperature dependence of resistivity of the films was typical as for epitaxial films, with insulator-metal transition between 260 and 300 K and sharp decrease of the resistivity below. X-ray diffraction analysis show (100) and (110) preferred orientation of the film. Transition electron microscopy revealed epitaxial grains with grain size about 100 nm distributed in polycrystalline matrix

Time evolution of LaxMnO3/normal metal point contact resistance

Resistance vs. time characteristics of LaxMnO3/normal metal junctions was studied in order to investigate the surface properties of epitaxial LaxMnO3 thin films. The change of the resistance of LaxMnO3/normal metal point contact was observed. The results are explained in the frame of oxygen out-diffusion from LaxMnO3 surface layer and creation of an insulating barrier from LaxMnO3 and/or metal

Spectral ellipsometry of La1-xMnO3 films with different degree of epitaxy

The dependence of the optical spectra of La1-xMnO3 films on the degree of epitaxy was investigated. Films of La1-xMnO3-δ (x ≈ 0.1) were grown by metal organic chernical vapor deposition on SrTiO3 and Al2O3 (r-plane cut) substrates. The films are supposed to possess a different degree of epitaxy because of various matching conditions between substrate and film lattices. The optical spectra were obtained in the range 0.5-5.0 eV by spectroscopic ellipsometry technique making use of photometric ellipsometer. Fine structure in the spectra of pseudodielectric function is discussed taking into account the excitations of Drude-type free electrons along with the charge-transfer 2 p(O) → 3d(Mn) and dipole-forbidden d-d(Mn3+) transitions. In this model the difference in the spectra of two type samples with different degree of epitaxy was considered

Effect of oxygen post-annealing on the magnetoresistance of highly epitaxial La0.7Ca0.3MnO3 thin films.

Epitaxial La0.7Ca0.3MnO3 (LCMO) thin films have been deposited by high pressure DC sputtering technique on SrTiO3 substrates. As-grown films exhibit metal - insulator transition temperature (T-MI) with values ranging from 131 to 220 K. The maximum value of the magnetoresistance is of about - 77% in a magnetic field of 0.5 T for T-MI = 131 K. The same films, annealed in a pure oxygen atmosphere, exhibit transitions to a metallic state at temperatures ranging from 210 to 284 K. Transmission electron microscopy analyses show a coherent growth between film and substrate

Growth and characterization of LaMnO3/SrTiO3 bi-layer

We report about LaMnO3/SrTiO3 bi-layers deposited by using injection metal-organic chemical vapour deposition (MOCVD). We have studied structure of the bi-layers by X-ray diffraction and its surface by AFM. Properties of the LaMnO3/SrTiO3 interface in fabricated LaMnO3/SrTiO3/Au tunnel junction were investigated by tunneling measurements. Obtained results are discussed with regard to suitability of MOCVD grown SrTiO3 film as a matenal for tunnel junction barrier