Surface pattern and large low-field magnetoresistance in La0.5Ca0.5MnO3 films

Formation of an ordered surface structure in La0.5Ca0.5MnO3 films due to the mismatch of the thermal expansion coefficient between the film and the substrate has been investigated. The surface pattern consists of grain chains located on regular orthogonal cracks. The cracks serve as weak-link grain boundaries, and unusually enhanced low-field magnetoresistance (−14.4% in 400 Oe at 90 K) has been observed, which may be explained by spin-polarized tunneling across the grain boundaries.