Abstract
Cobalt nanocrystals dispersed in rutile thin films on (0001) α-Al2O3 substrates are grown by pulsed-laser deposition. Their microstructure is investigated by transmission electron microscopy and their magnetic properties measured at temperatures from 5to350K. 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‖(100)rutile, and in-plane orientations of [112¯]Co‖[010]rutile and [1¯10]Co‖[001]rutile. The diameter of the Co nanocrystals is 4.4±0.15nm. The samples show superparamagnetic behavior at low temperatures. The zero-field-cooled magnetization versus temperature curve has a peak at about 105K. There is strong magnetic dipolar interaction between the particles which might have resulted in the observed hysteresis at room temperature.
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