SUPERPARAMAGNETISM AND DIFFERENT GROWTH MECHANISMS OF CO AU(111) AND CO/CU(111) MULTILAYERS GROWN BY MOLECULAR-BEAM EPITAXY/

The magnetization of Co/Au(111) and Co/Cu(111) multilayers grown by mo lecular-beam epitaxy has been measured. For ultrathin Co layers, super paramagnetic behavior is observed, very similar to that reported previ ously for granular samples. For somewhat thicker Co layers, hysteresis effects occur, indicating the absence of superparamagnetism. The clea r transition seen between these two modes of behavior is attributed to the growth of the Co particles from very small superparamagnetic clus ters to larger islands and ultimately to a film, as the thickness of t he Co layers is increased. Different magnetic properties are found for the Co/Au(111) and the Co/Cu(111) systems during the transition from granular to continuous layers. An investigation by reflection high-ene rgy electron diffraction suggests that this difference is mainly due t o the different growth modes of Co on Au(111) and on Cu(111).