Influence of misfit stress on the magnetoresistive properties of La0.7Ca0.3MnO3-delta thin films

For this study La0.7Ca0.3MnO3-delta (LCMO) films of various thicknesses wer e deposited on SrTiO3 (100), LaAlO3 (100), and MgO(100) substrates. The sub strate-film lattice mismatch causes changes in the microstructure of the fi lms and can therefore influence their magnetoresistive behavior. The struct ure of the films was characterized by x-ray diffraction and high-resolution transmission electron microscopy. Magnetic and electric properties were de termined using standard techniques. Samples grown on SrTiO3 show a strongly distorted growth. A large number of defects are incorporated in the initia l LCMO layers. Beginning at a thickness of approximately 500 nm films on th ese substrates show strong deviations in electric behavior and develop macr oscopic cracks. In the case of LaAlO3 substrates the films show only a few lattice defects. The substrate-film lattice mismatch is compensated by larg e stresses in the LCMO films. The best samples with the least amount of def ects are grown on MgO substrates even though the substrate-film mismatch is largest in this case. The misfit is completely compensated in a narrow reg ion near the substrate interface. From there on the LCMO grows with only fe w lattice defects and little strain. These films exhibit electric and magne tic properties similar to bulk materials. The results demonstrate that the colossal magnetoresistance properties of thin films are significantly influ enced by strain caused by the substrate. They behave different than bulk sa mples under hydrostatic pressure. These aspects must be considered when int erpreting the properties of such films and comparing the results of individ ual experiments. (C) 1999 American Institute of Physics. [S0021-8979(99)741 08-3].