Nanostructure and magnetic anisotropy of Co/Au multilayers

Multilayer Co/Au films were deposited on 40 nm Au underlayer by magnetron sputtering. The Co thickness is kept constant at 0.5 nm while the Au thickness is varied from 0.5 to 8 nm. Magnetic measurements show that me perpendicular anisotropy of the films changes from 3 × 10⁶ to 1.5 × 10⁶ erg/cm₃ as the Au thickness changes from 6 to 1 nm. Two films of (Co 0.5 nm/Au 6 nm)×9/Au 40 nm (denoted Au6) and (Co 0.5 nm/Au 1 nm)×50/Au 40 nm (denoted Au1) were examined by transmission electron microscopy. For the Au6 film, a bright-field image reveals the curvature of the multilayer. High-resolution electron microscopy shows dial the curvature consists of many atomic steps leading to a rough interface. The Au layer has the fee structure (ABCABC stacking) and the Co layer of two atomic layers interrupts the ABCABC stacking of Au and could be fitted to the AB stacking. In contrast to the Au6 film, the Au layers and the Co layers in the Au1 film cannot be identified in lhe high-resolution electron microscopy image. Bright field transmission electron microscopy images reveal the evidence of local clustering of Au and Co. A high density of 1/3[111]a dislocations is observed which supports the clustering argument. The anisotropy of the films is discussed in connection with the observed nanostructure involving the steps and the clustering of Au and Co.