Doping of interfaces in (La0.7Sr0.3MnO3)(1-x):(MgO)(x) composite films

Composite thin films of (La0.7Sr0.3MnO3)(1-x):(MgO)(x) (x=0-0.5) were grown on Al2O3 (0001) substrates by a metalorganic aerosol deposition technique. A columnar growth of the films with the predominance of (111)- and ((1) over bar 10)-orientation was observed. Pure films (x=0) show a Curie temperature of T-C=362 K, a metallic behavior accompanied with a low residual resistivity rhosimilar to10(-4) Omega cm at T=4.2 K and a very small low-field magnetoresistance. Low amounts of MgO doping, x=0.05, result in a totally different electrical transport behavior which is a pronounced low-field magnetoresistance MR=25% at T=4.2 K. The MgO was found to be located at the interfaces between the grains thus building tunneling barriers and enhancing spin polarized tunneling similar to a system with vertical artificial tunnel junctions. (C) 2002 American Institute of Physics.