Atomic Order and the Interaction of Electronic and Magnetic Subsystems in Epitaxial LaSr(Ca)MnO Films

We have investigated the structure, and electric, optical, and magnetic properties of LaSr(Ca)MnO films containing atomic clusters of various types coherently built into the basic crystallographic matrix. Below the transition to the metallic state, the electrical conductivity of the films is determined by tunneling of charge carriers between metallic clusters. We have found that for each sample there exists a threshold value of magnetic ordering, above which the magnetic subsystem starts to affect actively the film conductivity. The observed increase of conductivity with decreasing temperature is caused by the fact that in the process of magnetic ordering of the samples the cluster size and concentration of metallic phase increase. Experimental results are in agreement with theoretical calculations.