Magnetic field dependence of conductance and conduction noise of an artificial grain boundary junction in a La 0.67Ba 0.33MnO 3 epitaxial thin film

Abstract

A single artificial grain boundary in La 0.67Ba 0.33MnO 3 (LBMO) thin film has been prepared by depositing the film on a bicrystal substrate using laser ablation technique. We investigated the magnetic field dependence of magnetoresistance and conductance–voltage characteristics of the grain boundary at 77 K. A decrease of nonlinearity of current–voltage characteristics was observed upon application of magnetic field. The results are explained by assuming the presence of two different types of parallel conducting channels (metallic and highly resistive) across the grain boundary. The analysis of the results reveals that the application of magnetic field suppresses magnetic disorders at the grain boundary region and increases metallic conduction channels across the grain boundary. The temperature dependence of the conduction noise of the bicrystal grain boundary was measured at 0 and 1.5 kG magnetic field and compared with a microbridge on the LBMO film having no grain boundary. The presence of the grain boundary was found to enhance noise by one order of magnitude. The noise of a bicrystal grain boundary showed a decrease in the presence of 1.5 kG magnetic field for T<210 K. This decrease of noise confirms that the application of a magnetic field induces more metallic channels across the grain boundary.