Impact of granularity on transport properties of mechanically stressed La0.67Ca0.33MnO3 films

(La,Ca)MnO3 is one of so called collosal magnetoresistive materials and it is of interest to correlate its transport properties to film growth in order to optimize its performance. Two-hundred nanometers thick (100)La0.67Ca0.33MnO3 films were grown by laser ablation on (100)SrTiO3, (100)LaAlO3 and (100)(LaAlO3)0.3+(Sr2AlTaO6)0.7 substrates. The films were granular in structure with low angle boundaries between the grains. The volume of the unit cell was considerably smaller for films grown on a SrTiO3 substrate than on LaAlO3. At temperatures higher than the one where the spins order, the strongest response of resistivity on temperature ρ(T) was measured for those (100)La0.67Ca0.33MnO3 films that had the smallest volume of the unit cell. An increase of the lattice parameter for a film was accompanied by a decrease of the resistivity. The films grown on (LaAlO3)0.3+(Sr2AlTaO6)0.7 substrates had the best crystallinity and the largest magnetoresistance.