0.6 BaTiO3-0.4CoFe(2)O(4) (BTO-CFO) composite thin films were deposited under various working pressures on SrTiO3 (100) substrates by pulsed laser deposition. The phase separation and the microstructure of the composite film were investigated by x-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy, and energy dispersive x-ray spectroscopy. The separation of the BTO and CFO phases started at a lower substrate temperature and full width at half maximum values for BTO and CFO were smaller in the heteroepitaxial composite film deposited under a low working pressure of 0.1 mTorr than the composite film deposited under 100 mTorr. The BTO-CFO heteroepitaxial nanocomposite film exhibited a typical 1-3 nanostructure, rectangular-shaped CFO nanopillars with a lateral size of 20-50 nm embedded in the continuous BTO matrix phase, when deposited at 750 degrees C under 0.1 mTorr. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3429597]