Effect of different seed layers with varying Co and Pt thicknesses on the magnetic properties of Co/Pt multilayers

Abstract

Magnetic and structural properties of Co/Pt multilayers with varying Co (tCo) and Pt (tPt) thickness grown on various seed layers have been examined. It is challenging to grow Co/Pt multilayers as a top electrode with high perpendicular magnetic anisotropy (PMA) for magnetic tunnel junctions which usually comprise of CoFeB/MgO/CoFeB. We show that a thicker Pt layer of 1.2 nm is necessary to attain effective anisotropy (Keff) up to 0.14 MJ/m3. On the other hand, Co/Pt multilayers with high PMA have been achieved for proper textured seed layers of Ru and Pt. In the case of Ru seed layer, a higher Keff = 0.45 MJ/m3 can be achieved for tCo = 0.5 nm and tPt = 0.2 nm. This can be attributed to the lower lattice mismatch (∼4%) within the multilayers and hence a more coherent CoPt (111) structure. Finally, we note that the film roughness could play an important role in influencing the PMA of the multilayers. The highest Keff ∼ 0.6 MJ/m3 is achieved for Pt seed layer.