Anisotropic magnetoresistance and magnetic properties in La0.67Ca0.33MnO3 thin film by sputtering

La0.7Ca0.3MnO3 thin films grown on SrTiO3 (100) substrates by off-axis sputtering technique exhibit a fully strained film when the thickness of films is thinner than 25 nm. Transport and magnetic properties of the films for the magnetic field applied parallel to the surface of the films were consistent and could be easily explained by the domain-rotation model. However, these properties were not consistent when the field applied perpendicular to the substrate. The critical field for which peak resistivity was observed in the magnetoresistance measurement, H-c'(perpendicular to) similar to 79,500 A m(-1), one order of magnitude higher than the coercive field, H-c(perpendicular to) similar to 7950 A m(-1). The peak width of the in-plane X-ray diffraction peak (200) of the films as measured by a five-axis X-ray diffractometer showed an exponential decrease to the thickness of films. This broadening cannot be explained by the strain effect alone. We found that nanostructures, such as the ferromagnetic phase segregation in the paramagnetic matrix or the columnar structure in films that introduced excess domain walls, could be responsible for the inconsistency between H-c'(perpendicular to) and H-c(perpendicular to). (c) 2006 Elsevier B.V. All rights reserved.