Epitaxial ruthenium dioxide (Ru O2) chromium dioxide (Cr O2) thin film heterostructures have been grown on (100) -TiO2 substrates by chemical vapor deposition. Both current-in-plane (CIP) and current-perpendicular-to-plane (CPP) giant magnetoresistive stacks were fabricated with either Co or another epitaxial Cr O2 layer as the top electrode. The Cr2 O3 barrier, which forms naturally on Cr O2 surfaces, is no longer present after the Ru O2 deposition, resulting in a highly conductive interface that has a resistance at least four orders of magnitude lower. However, only very limited magnetoresistance (MR) was observed. Such low MR is due to the appearance of a chemically and magnetically disordered layer at the Cr O2 and Ru O2 interfaces when Cr2 O3 is transformed into rutile structures during its intermixing with Ru O2. © 2005 American Institute of Physics.