Microstructure and inter-grain magnetoresistance in Ag-doped polycrystalline La0.67Sr0.33MnO3 thin films

Ag-doped La0.67Sr0.33MnO3 thin films with various Ag concentrations were deposited on (001) LaAlO3 substrates at 400degreesC by using a dual-beam pulsed-laser deposition system. The Ag-doped films show polycrystalline structure with epitaxial c-axis columns. These columns were composed of closely arranged polyhedra of size 10-15 nm, resulting from the enhanced stress-induced grain boundary diffusion. In the case of heavy doping, tiny separated Ag crystals were observed at grain boundaries. Due to the interaction between the two laser-induced plumes, the Ag precipitation also helped to form anomalous clusters consisting of nano-sized grains and amorphous phase. By adjusting the deposition conditions carefully, we can tailor the microstructure of the film and correspondingly alter the resistivity and the inter-grain magnetoresistance of the Ag-doped films. Theoretical simulation led to results consistent with the microstructure observations and the magnetoresistance measurements.