Magnetoresistance and magnetic viscosity of La0.7Ca0.3MnO3 films

Magnetoresistance and magnetisation relaxation measurements are reported on a series of La0.7Ca0.3MnO3 films produced by pulsed laser deposition. The films were grown on single crystal substrates of LaAlO3, Si and LSAT. Measurements were made on the film grown on Si in the as-deposited state; measurements on films on the other substrates were made before and after anneal. The polycrystalline film on Si showed a drastically increased resistivity as well as a large, low held magnetoresistance. The magnetisation for all films decayed logarithmically with time after a sudden magnetic field change. The magnetic viscosity was temperature independent below about 50 K and varied linearly with temperature in an intermediate regime up to a maximum below the Curie temperature. The average activation volume of all films was estimated and found to be independent of the microstructure; it increases with temperature and is of the order of the cube of the Bloch-wall thickness. This result suggests that the large, low held magnetoresistance in polycrystalline films is not due to domain-wall scattering. (C) 1999 Elsevier Science B.V. All rights reserved.