Crystallographically orientated fcc Co nanocrystals in rutile TiO2 thin films

Cobalt nanocrystals dispersed in rutile thin films on (0001) alpha-Al2O3 substrates are grown by pulsed-laser deposition. Their microstructure is investigated by transmission electron microscopy and their magnetic properties measured at temperatures from 5 to 350 K. The Co nanocrystals have fcc structure with no multi-twin defects and are crystallographically orientated with their (111) planes parallel to the substrate surface having an orientation relationship to TiO2 of (111)(Co)parallel to(100)(rutile), and in-plane orientations of [11 (2) over bar](Co)parallel to[010](rutile) and [(1) over bar 10](Co)parallel to[001](rutile). The diameter of the Co nanocrystals is 4.4 +/- 0.15 nm. The samples show superparamagnetic behavior at low temperatures. The zero-field-cooled magnetization versus temperature curve has a peak at about 105 K. There is strong magnetic dipolar interaction between the particles which might have resulted in the observed hysteresis at room temperature. (c) 2006 American Institute of Physics.