Magnetic and structural properties of annealed CoPt/C multilayers

Abstract

The structure and magnetic properties of multilayer Co 82Pt 18/C films with equal CoPt and C layer thickness have been studied as a function of annealing temperature and film thickness. In general, annealing leads to the breakup of the continuous films and the formation of a laterally heterogeneous morphology consisting of separate CoPt and C regions. For individual layer thickness ⩾5.3 nm, annealing has no significant effect on the crystallographic structure and magnetic properties of the films. In both the as-deposited and annealed states, the films have HCP structure with perpendicular c-axis orientation and exhibit perpendicular magnetic anisotropy. The structure of these films appears to be associated with the growth of the CoPt on the C layers. For films with individual layer thickness of 1.3 and 2.7 nm, the structure and magnetic properties are strongly affected by annealing. In the as-deposited state, films have a fine grain structure and coercivities of a few Oe. Annealing leads to the breakup of the multilayer structure at about 300°C and the formation of ∼20 nm HCP and FCC magnetic grains, with the HCP grains exhibiting in-plane c-axis texture. Annealed films have large in-plane coercivities (maximum of 2.77 kOe) and random in-plane magnetic anisotropy. The increase in coercivity with annealing temperature above ∼375°C is primarily associated with an increase in switching volume.