  Many unusual behaviors in complex oxides are deeply associated with the
spontaneous emergence of microscopic phase separation. Depending on the
underlying mechanism, the competing phases can form ordered or random patterns
at vastly different length scales. Using a microwave impedance microscope, we
observed an orientation-ordered percolating network in strained Nd0.5Sr0.5MnO3
thin films with a large period of 100 nm. The filamentary metallic domains
align preferentially along certain crystal axes of the substrate, suggesting
the anisotropic elastic strain as the key interaction in this system. The local
impedance maps provide microscopic electrical information of the hysteretic
behavior in strained thin film manganites, suggesting close connection between
the glassy order and the colossal magnetoresistance effects at low
temperatures.
